Troubleshooting and Maintaining Your RV’s Air Conditioner
The rooftop air conditioners used on motorhomes are made to give many years of dependable cooling efficiency, especially if you maintain them.
This article has two parts: first, how to troubleshoot your AC and decide which parts to replace or service; and second, how to maintain your AC.
These repair and maintenance tips are very simple to follow, even for those without much hands-on experience.
Part 1: Troubleshooting
Some Background: How Your AC Works
If you are unfamiliar with how a motorhome air conditioning system works, this companion article will help you understand which parts of the motorhome rooftop air conditioner unit to check, service, and repair.
Briefly, your air conditioner, which may be combined with a heating system, includes a compressor—to circulate a cooling fluid like Freon through the coils and fins of the condenser—and a fan, to blow cooled air through the RV. The fan and compressor are turned on and off by a thermostat—a switch attached to a thermometer—and kick-started by one or more capacitors. The thermostat and other controls are run by the vehicle's 12-volt electrical system.
Where to Start Investigating
Many problems your air conditioner might have—sluggish behavior, turning off prematurely--can be resolved by checking out the electrical system in order, going first through the possibilities that are easiest to resolve. These easier choices often solve the problem. If they don't, you can investigate further so you can decide if you need to replace the big items like the fan and the compressor or get a whole new AC unit.
First, we'll address the common electrical issues.
A Precaution
Before attempting any maintenance or repairs on the rooftop AC unit, be sure to switch off the electrical supply to the unit, either by tripping the breaker or by unplugging the motorhome from the electrical receptacle.
RV AC Issues You Can Troubleshoot Yourself
- If your AC does nothing and makes no noise, make sure your unit and its controls are getting power.
- If your AC fan or compressor is slow to start, doesn't blow any air, blows weakly, blows only warm air, stops after a while, dims your lights, or trips your breaker, you should first check your capacitors and replace them if needed.
- If there's no air blowing, check the fan capacitor; if there's no cooling, check the compressor capacitor.
- If the capacitor is okay, you should look at whether the thermostat is getting power by checking whether the 12-volt appliaces work.
- You can check the function of the thermostat if it's wall-mounted. If the unit only works when thermostat wires are touching, the thermostat is bad. The thermostat is easy to replace.
- If the capacitor and thermostat are okay, the control board may be bad.
- If the control board is okay, you may have to replace the fan motor or the compressor.
- If the fan only works at certain speeds, the fan motor may be bad.
- You can have the fan motor rebuilt (if it's not the sleeved-bearing type). Or you can replace the fan motor yourself if the unit is in good shape otherwise.
- If the compressor is bad, it should probably be replaced, not fixed.
- If your system drips or overheats, the coils may need cleaning.
- If the roof AC leaks, the bolts may be loose or the gasket may be leaking.
- If the system is very cold or ice builds up, it may be low on Freon.
- If the unit is noisy, something out of place may be interfering with its motors; you can check by removing the shroud.
The First Step: Is There Power?
If your unit does not react at all—does not go on and does not make noise—you will want to make sure it is getting power. Look in the 12-volt panel and check that the fuse has not blown or the breaker has not tripped. The 12-volt power system runs the controls to the AC including the thermostat.
Running the AC unit itself draws a lot of higher-voltage power, maybe too much for a 15-amp power pole, and if there are two modern rooftop units they may draw too much for the 30-amp power supply provided at many campgrounds. If the unit draws more than the system can provide, the breaker or fuse will shut off. Fortunately, many campgrounds and RV parks now provide 50-amp service for modern multi-unit AC systems.
The thermostat is run by 12-volt power, like your motor home's lights and vent fans. If these accessories aren't working either, there is something wrong with the 12-volt power. A breaker may be bad or there may be a loose connection in the breaker box. Occasionally the power converter that converts your higher-voltage power to 12-volt power is bad.
Next: Consider the Capacitors
If the fan or the compressor fail to start, it is possible the starting capacitor is malfunctioning. A bad capacitor can cause a variety of symptoms: the AC unit merely hums and "tries" to start, it runs a few minutes then trips a breaker, the fan won't start without a push, or it blows only hot air because the compressor can't start.
The capacitor stores electricity to give both the fan motor and the compressor an extra boost whenever the RV AC unit starts. It is not unusual for the capacitor to go bad, especially if the RV sits unused for a while, and not be able to provide that little push that gets the motors going. On occasion a bad capacitor will explode with a puff of smoke without damaging the rest of the unit.
There may be one capacitor for both compressor and fan, two capacitors (one for each part), or even three or more all together. A capacitor is often shaped like a small battery, flask, or button.
If you have a multimeter in your tool kit, you can use it to test the capacitor. A good capacitor should show a random value on the multimeter that slowly decreases the longer you keep the probes in place.
A bad capacitor is easy to replace. Check the required voltage and model numbers on the old capacitor when ordering a new one.
When replacing it, make sure the power is off. Observe which wires go into it where, and make a note so you can install the new one exactly the same way. Don't touch its terminals with your bare hands. Before you throw the old capacitor away, drain out its electrical charge by connecting its terminals with a screwdriver (make sure the screwdriver handle you are holding is insulated).
Very often, your AC unit will start and run fine after you replace a capacitor.
Next: Check the Thermostat and Switches
A bad thermostat is another possibility. If you have a wall-mounted thermostat, you can check it by checking its voltage with your multimeter. If the unit only goes on when you touch the thermostat wires to each other, the thermostat is definitely bad.
If the thermostat and capacitors are all okay but the AC still doesn't work, you may have a bad control board.
Thermostats and switches may be purchased online by finding the correct model and serial numbers before ordering the new parts. These items are easy to replace in most cases. As always, make note of and remember the wiring connections when replacing these electrical components.
Is Your Fan or Your Compressor Bad?
If after you check these electrical items your AC still doesn't blow out air, or it blows only at certain speeds, your fan motor may be bad. If your AC blows but only hot air comes out, your compressor may be bad. Sometimes—not necessarily—a fan or compressor smokes or leaks oil when it goes bad.
A compressor that is working should turn on audibly and feel warm to the touch. You can test a compressor with a clamp-on ammeter, if you can rent or borrow one. Check how many amps the compressor is drawing. If it draws much more current than the amp rating written on the unit or on a nearby plate, the compressor is toast.
You May Be Able to Rebuild or Replace Your Fan Motor
Oiling your fan motor, as shown in Part 2 of this article below, will help it run more easily. If your AC fan motor is slow to start even after oiling, or needs a nudge to get it going, or only runs at certain speeds, or doesn't run at all, it will need to be rebuilt or replaced.
Fan motors come in two types: with exposed bearings which may be lubricated easily or with sleeved bearings (see the last photo in the article). The first type of fan motor may be rebuilt fairly cheaply and will last for many more years. But not so a sleeved-bearing AC fan motor.
Unlike fan motors with bearings, a fan motor with sleeves cannot be rebuilt economically, and must be replaced with a new one if it goes bad.
If your AC unit seems to be in pretty good shape otherwise, you can order a new AC fan motor to fit your particular unit. There are many sizes and models to choose from. Check the numbers on your old motor. By looking at pictures and descriptions on Amazon you may be able to identify a universal motor that will fit your unit.
Replacement of the AC fan motor is a simple job requiring only a few tools. If the electrical connection to the motor isnt a simple plug-in, mark down the colors of the wires before removing the old fan motor.
Test the new fan motor, before replacing the AC shroud, to check for proper alignment and fan clearance.
Removing and Replacing the Fan Motor
A Bad Compressor Isn't Usually Worth Fixing
If, after you determine that the switches, capacitor, and relays are not at fault, the RV AC compressor fails to operate correctly and cool your air, it is usually better to just junk the unit and buy a new one.
Unless you have access to a used compressor and have the means to replace it and recharge the system yourself, it will likely be too expensive a repair. Under normal circumstances a compressor will last much longer than its warranty.
It May Be Simpler to Replace the Whole AC
If after investigating these possibilities you decide your old RV AC unit has enough problems to need replacing, please see my article on how to install a new rooftop RV AC unit. Replacing your old unit with a more efficient RV AC unit is a very simple and quick procedure you can do yourself.
Some Miscellaneous AC Problems and What May Cause Them
If your AC does run, but only with problems—overheating, dripping, being way too cold—you can address these problems too.
- Overheating may be due to a simple failure to clean the coils—something I show you how to do in the second half of this article. When the coils are clean they can disperse excess heat into the air.
- If water leaks into your unit and seems to come from the AC, investigate to see where it is coming from. The leak may come from the gasket between the unit and the roof; if so, it's easy to address. Tighten the bolts carefully, and if that doesn't work, replace the gasket.
- Dripping from the unit itself may be caused by water condensing in the wrong place (in the pan under the air conditioner) instead of being evaporated by the fan. Such water buildup may be due to dirty coils, and if so, you can cure it by cleaning the coils.
- If your unit blows very cold and builds up ice—and especially if it later stops cooling at all—it may be low on Freon. Sometimes you can see a visible oily residue around a Freon leak. You may be able to add Freon to your system yourself with a self-piercing valve.
- If your motor is noisy, you can investigate the problem by taking the shroud (the cover) off the roof AC unit and seeing if everything is in place. The rubber shock absorbers on the compressor and fan may be interfering with the motion of the unit.
Part 2: Maintenance
Accessing the Condenser and Evaporator Coils to Clean Them
Maintenance gives your AC longer life and better efficiency. Roof air conditioning units on motorhomes are the same as ones used on other types of RV campers such as travel trailers and pop-up campers. These repair and maintenance procedures are identical for all these types of campers.
After a few seasons of use, it isn’t unusual for the AC unit to not cool the motorhome as quickly or as efficiently as it once did. Even if you clean the filters regularly, the evaporator and condenser coils will eventually become coated with dirt and grime, which inhibits airflow and cooling efficiency.
Before attempting any maintenance or repairs on the rooftop AC unit, be sure to switch off the electrical supply to the unit, either by tripping the breaker or by unplugging the motorhome from the electrical receptacle. You are now ready to remove the RV AC shroud (above) by unscrewing the four bolts securing it to the RV AC unit itself.
How To Clean the RV AC Coils
After removing the AC shroud you will be able to see the evaporator and condenser coils on either end of the RV AC unit.
If they appear similar to those in the photos above then they need a thorough cleaning to allow unrestricted airflow through them.
Although regular household cleaners may clean the coils to a certain extent, AC coil cleaners made especially for the purpose, like ZEP Foaming Coil Cleaner, will remove the grime build-up much more efficiently and will not harm the coils themselves.
Follow the instructions carefully for the best results. A good wet/dry Shop Vac will help you clean up afterward and remove any excess cleaner or grime from the RV AC unit.
Use a 
These fin combs are very inexpensive and may be used many times in the future on both RV and home AC coil fins.
Straighten out those bent coil fins and increase the efficiency of your A/C unit.
Maintaining the AC Fan Motor
While the RV AC shroud is removed, it is a good time to service the fan motor and clean the fan itself. Whether your RV AC unit is made by Coleman, Carrier, Duotherm, or Dometic, it will have one fan motor which turns both the squirrel-cage fan and the heat exhausting fan.
This motor should be oiled at this time.
If your RV AC fan motor has regular bearings, there will be oiling ports at each end of the motor. It may be necessary to remove the metal sheeting over the top of the fan motor, plus a few sheet metal screws, to access the bearing oiling ports.
If no oil ports are evident, then your motor has sleeves instead of bearings. You may still oil the shaft at the point where the sleeves enter the fan motor housing. The oil will seep inside and help the fan motor last much longer.
Covering Your Motorhome AC Unit in the Off-Season
Your motorhome AC unit should give you many seasons of dependable operation if serviced annually. It's good to put a cover over the AC unit during the times when the motorhome is not in use.
These inexpensive RV AC covers protect the unit from moisture, extreme cold or hot temperatures, and debris from storms, birds, and insects. They will more than pay for their cost over time.
This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.
Related
How to Find and Inspect Used RVs, Pre-Owned Campers, and Travel Trailers (With Checklist)
How to Install a Coleman RV Rooftop Air Conditioner
Troubleshooting and Repairing RV Electrical Problems for the Beginner
Your RV Generator and How It Works
RV and Camper Rooftop Air Conditioner Maintenance, Troubleshooting, and Repair
Comments
- AUTHOR
Roy, this rules a bad motor out. It could be the ignition system, but then, it may not be. Sorry, as I said earlier I'm no expert on furnaces. I'd ask someone at your local A/C repair shop.
Randy
Thanks, Randy. I have a Suburban SF20 furnace. I started it up two weeks ago with no issues. Then, two days ago, after it ran for about thirty minutes, I started hearing a strange "hum" sound from the unit. It got increasingly louder.
Thinking it was a bad bearing in the motor, I shut it off and began to research about the unit. This morning, I turned it on again...no problems until about fifteen minutes of it running...the same "hum."
I then noticed when I turned the thermostat heat setting to "Off," the hum instantly stopped while the motor kept blowing until it, too, finally shut off. No strange noises from the blower when I turned the thermostat to "Off."
I don't believe it is a problem with the blower motor and am figuring it has to have to do with the propane hardware that might be causing this odd hum. I recorded this "hum" on my iphone and you can hear it clearly. Any ideas?
- AUTHOR
Hello again, Roy. I'm not an expert on furnaces, but if you'll tell me the problem I'll give youmy two cents worth.
Randy
Hi Randy:
You have helped me in the past with my Coleman Mac AC unit, but I'm wondering if you are knowledgeable about Suburban furnaces in RV's as well?
- AUTHOR
Dan, this does indeed sound like the generator isn't furnishing enough amperage to run the AC properly. You'll need to borrow or rent an amp meter to check the generator properly.
Randy
- AUTHOR
Dan, could be a low Freon charge, but it could also be the control board or the stat causing this.
Randy
Randy, my unit is 15 years old. It would have a hard time starting or the compressor would quit and only the fan would operate. I have replaced the capacitors twice in one year but now the fan and compressor will not kick on. This seems to occur when I would run the 4000 Onan generator while driving. The breaker will now pop when I try to run the AC on either shore power or the generator. I have purchased a new Mach III 15K with the assumption that the compressor is bad and is requiring a significant draw from the generator.
Have you heard of this before? What is the best way to test the generator to make sure it is producing enough power to start the AC unit?
Thank you
My unit cycles on and off frequently even at night
- AUTHOR
Jack, this could be several things. Dirty coils can cause the breaker to trip when the airflow over the compressor isn't enough to keep the compressor cool.
It could also be a weak capacitor or a bad compressor. I'd clean the coils first and then test the capacitors if the cleaning doesn't do the job.
Randy
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My AC unit runs for 20 minutes and then throws the breaker. Is this the capacitor or dirty coils? Thank you
- AUTHOR
Jeff, I was referring to the thermostat. You may have a wall mounted thermostat, or it may be contained in the board you mentioned. It's not uncommon for a stat to go bad.
Randy
and what bothers me is even the mode fan is not working...
Thanks for the quick answer, and the stat, what is it exactly?
- AUTHOR
Jeff, if you're getting power to the board, there may be a short or a bad relay in the board itself. Depends on what is contained in the board. Also, if one thermostat controls both heat and AC, the stat may be bad.
Randy
Randy
Hi Randy,
Motorhome 2010, have a board that runs A/C, Fan and Heat. Nothing is working. 12 volts is working on other appliances and fuse/breaker are ok. What do you think it is?
Hi. Wonderful article. We want to purchase a reverse cycle conditioner for our motorhome. We prefer free camping. Any suggestions. Thank you
- AUTHOR
Brent, it's your call. I cannot guarantee it will fix the problem, but it's good guess.
Randy
For the coleman mach units, it looks like the correct part is a 46374: junction control box assy. With circuit board. Do you think its worth replacing to see if it fixes the issue before taking it for service? It's only $55. Thanks Randy.
- AUTHOR
Brent, the control board isn't serviceable per se, but it's easy to change out if it is indeed the problem. It can affect the speed of the fan or the compressor action.
Randy
Are the ceiling knob-type thermostats changeable? Thats what this unit has. Also, the coleman mach 15 has no serviceable control board shown on diagrams and parts store can find no listing. Thank you.
- AUTHOR
Brent, it could be the control board if you believe the thermostat is okay. Not sure the temp or humidity sensor is the issue but you can check it anyway.
Randy
I was reading that sometimes the temperature or humidity sensor that is clipped onto the coil sometimes gets jarred loose. Could that be causing the problem? Thank you.
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Randy,
I tested my capacitors and both check okay. Where should i go from here? My fan still continues to blow at different speeds. No problems with the fan at startup, but after being on for awhile it begins blowing at different speeds.
- AUTHOR
Melodie, The caps may still be weak and may shut the AC down again. If so, search online at Amazon to see what capacitors look like.
You should clean the coils every two years or so if you use the camper a lot in the summer.
Randy.
Randy,
Thank you so much for getting back to me. After all my reseach I was wondering about a bad capacitor(s). Do you have any links to explain how to find where they located in the unit?
Also, as an update......when we got home, after letting just the fan run all day, the AC did kick in when we turned it on and we do have cold air and it seems to be draining as normal from the outside drain line. Do you tnink it might still be capacitor(s)?
And, we did use coil cleaner last night. I forgot to add that as one of the last steps we did. How often should we expect to use the cleaner in weather conditions of the Tampa area and run the AC a lot?
Thanks again, for your feedback!
Melodie
- AUTHOR
Melodie, this may be a bad capacitor or perhaps two of them. These are easy to replace and relatively cheap, around $25 or so. Any AC or electric motor repair service can test and furnish replacement if they're bad.
The most common cause of moisture leaking down inside the camper is because of the coils being dirty and clogged. The fan cannot disperse the excess moisture into the air and the AC will not cool efficiently and may cause the compressor to overheat and shut down.
Go online or to a Lowe's, Home depot or ACE Hardware store and get a couple of cans of spray no-rinse coil cleaner and follow the instructions.
Randy
Hello,
Post is a little long - just want to be sure and share all the things we have tried to help get the best feedback.
We have a 2004 Fleetwood Pride with a Coleman Mach Air AC unit with the following issue
AC will not turn on - Fan will run
Here are the steps in when the issue happened and what we have done:
1. We are full timers in Florida and new to 5th wheel living
2. Recently, have noticed condensation leaking from ceiling vent area.
3. We keep the thermostat set at 78-80
4. Keep fan on high
5. Yesterday late afternoon AC just stopped
6. When we realized it should have kicked back on - we lowered the temp just a bit to double check.
7. AC and fan - neither would kick back on
8. Did a reset - electrical panel, off for 30 seconds, no response.
9. Noticed that ground where unit drains to was unusually drier than normal - also, no condensation dripping inside like it had for the last few days
10. Left unit off for a couple of hours thinking it may have frozen.
11. Repeated reset and did get fan back on. Turned AC on which then made fan go back out.
12. Repeated reset and left off for another hour or so.
13. Turn on fan only on high for the night
14. Turned AC on and only a clicking sound - about 4-5 click from thermostat - no AC and again now no fan.
15. Repeated reset and left off for about 30 min.
16. Fan back on - set to high
17. Have not tried anything else at this point
Any tips and advice much appreciated!
Good question. I'll have to double-check. I assumed they were controlled separately. Its a 2004 29ft Fleetwood. Model# 2952BS. I've been the sole owner. I'll check the system and get back to you. Thanks
- AUTHOR
Sherman, both the AC and heater thermostats are powered by the 12 volt system. Does one control box handle both AC and heater?
Randy
- AUTHOR
Mike, this either a thermostat problem or a control board issue. Check the stat before replacing the board.
Randy
Colemon A/C and gas heater dont work. Heater startup board verified good. Replaced thermostat. Replaced battery. Not sure if both are connected or separate problems that happened at the same time. 12 volts is good at the thermostat. isolated thermostat at AC unit control box and heater still did not work. Plug to external ac power and good 12 volts and disconnected converter still no a/c or heat?
When I turn on my furnace the air conditioner comes on. How do I resolve this issue. Any ideas would be appreciated
- AUTHOR
Dennis, yes there should be a breaker or fuse for the AC in the main panel. There may be something else on the circuit as well.
Randy
Just replaced my Coleman Mach 15000, new junction box, new breaker and new thermostat. It’s just the ac without a heat pump.
The heat part of the thermostat works the heat but when I try the ac neither the fan or compressor works. Where do I go from here?
Is there a fuse on my main panel that goes to the ac?
- AUTHOR
Brent, you can test the caps with a multimeter set on ohms. When the probes are touched to the terminals you should get a random number decreasing in value as you continue hold the probes to the terminals.
A zero or steady number means the cap is weak or bad.
Randy
Hi Randy,
I'm having the same problem as before when i changed the capacitors and then it was running fine for two trips. A/C is blowing at different speeds again with an aubible beeping coming from inside during the slowdown. Ive since invested in a surge guard and watching it while it running it will sporadically draw 48amps?? Then go back down. Do you think my capacitors are bad again? Thank you.
- AUTHOR
Craig, you got me! The compressor needs to be running--or trying to--to get an amp reading on it. You think you can get an amp reading in less than 15 seconds?
Randy
Randy thank you. I have another question. I only replaced the capacitor and not the fast start piece on the top of the capacitor. Could that blow the capacitor as well? The new capacitor did turn the compressor on but after 15-20 seconds it blew the capacitor. Looking at the original cap and fast start - it seems to have fried the fast start piece as well as blowing the cap. I have looked at the wires that I could see and dont see any fraying or burning marks nor do I see any kinks or breaks in the plastic surrounding the wires. How do I check the compressor without putting in another capacitor and blowing it?
- AUTHOR
Debbie, you can get a replacement Capacitor at any AC or electric motor repair shop. They can test it and furnish you a replacement. About $25. Don't touch the terminals on the caps before discharging them with an insulated screwdriver incase it still holds a charge.
Randy
- AUTHOR
Craig, you may have a bad compressor. The only way to tell for sure is to use a clamp-on amp meter to see if the compressor is pulling more amps than normally required. Usually though, a bad compressor will trip the breaker instead of blowing the cap. It may be a short as you suggested, but the only way to tell is to look for it.
If you find the problem, please let me know so I can help others with similar problems.
Randy
Hi my ac only clicks when I turn the thermostat on and I’ve been up top checked my capacitor and one is receiving no power. What do I need to do to fix it?
Hello Randy,
great read and thank you for the help on here. I found that I had blown a capacitor so I replaced it. Fired up the unit, turned on for about 20 seconds then the capacitor blew again. Not sure where to begin. I have a 2000 Fleetwood flair. Acts like a short but from where is beyond me. Do you have anything that can help point me in the right direction?
- AUTHOR
Jeremy, Glad you found the short! Beats having to install a new unit. Enjoy your "cool" weekend. :)
Randy
Randy
Thanks for the reply!
After speaking with a service tech at the dealership, he advised that it was highly unlikely that a bad cap would make the breaker trip immediately upon plugging the camper in and that it sounded like a direct short possibly as a result of melted wires from under-current at a camp site.
I pulled the shroud off from inside the camper and up inside the return air is the control module. I removed the wing nuts, dropped it down and immediately noticed the problem. The 12-2 wire was burnt where it went into the grey cable connector and into the control box. Apparently, upon install, the factory nicked the wires, heated up and shorted out. There was enough extra wire that I was able to cut it off and wire it all back together - everything is working great again!
Weekend disaster averted.
Thanks again for your reply!
- AUTHOR
Jeremy, you may have a bad capacitor. Cheap and easy to replace if it is bad. Any local AC or electric motor shop can test and replace them for you.
Randy
Hey Randy
I have a 2019, 50 amp, camper with an Airxcel Coleman Mach 15 AC unit that has worked great the few times we've used it this summer.
I just plugged it in to get ready for a trip and it immediately tripped the 15 amp A/C breaker AND the 50 amp main breaker inside the camper. I then opened both breakers and just turned on the main - everything else in the camper works perfect, including the rear AC...
I made sure the thermostat on the wall was off, then again tried to close the 15 amp A/C breaker and "POP" same result - both main and AC breakers tripped.
When the AC breaker is off and I toggle the thermostat, I can hear the faint clicking noise in the AC unit itself so that tells me the thermostat is getting power correct?
I know it's still under warranty but the dealer can't get to it for two weeks and we are supposed to be leaving Friday!
Any ideas on what could be causing this?
- AUTHOR
David, the single cap may not be furnishing enough power to start and run both fan and compressor. You can test the cap yourself if you have a multimeter.
Set it on OHMS and put the probes to the terminals. If the cap is good you should get a random number decreasing in value the longer you keep the probes in contact. No number, or an unchanging number means the cap is bad. Hope this helps.
Randy
I'm not for sure. I looked at it myself before I called them and it looks like the fan capacitor and compressor capacitor are the same capacitor. The fan is running fine so I assumed the capacitor was fine as well.
- AUTHOR
David, did they check the compressor capacitor, or do you know? A bad compressor capacitor will cause the compressor to not start and run properly.
About 25 bucks and easy to change, it may be worth a try. Personally, I get quite a few questions from Dometic AC users and haven't noticed any increase in compressor's going bad in their units.
Randy
Randy,
My Dometic unit is blowing hot air or outside air. Had a repair service come out and look at it and they said it was the compressor and want to put a new unit on. My camper is a 2016 model and I find it hard to believe the compressor has already gone bad. They claim they have had other Dometic compressors gone bad and it must have been a bad batch. Should I get a second opinion or just let them install a new unit?
- AUTHOR
Jason, the covered coil is the one usually causing the fan motor to overheat as it's the one the filter is supposed to keep clean. Over the years this coil can get really dirty.
Try some no-rinse foaming coil cleaner from Home Depot, Lowes, or Ace hardware. If this doesn't solve the problem then I'd checked the compressor and capacitors.
You can do this with a digital multimeter set on ohms. If the cap is bad you'll get no number or a steady random number. If the cap is good you'll get a random number which decreases in value as you keep the probes on the terminals.
You'll need to borrow or rent an amp meter to check the compressor to see if it's drawing more amps than required. This info should be on the compressor itself or on a plate nearby. Hope this helps.
Randy
My Mach 3 AC units tripping breaker intermittently after running 10 min - many hours. I replaced both breakers (20A). I can run fan without AC endlessly without tripping breaker. I had shroud off and the coil that was accessible without removing the inner metal shroud was clean. I’ll have to check that coil that’s hidden maybe very dirty. You think I should look into capacitor replacement? Both units cool air very well. Maybe a hard start kit? Any way I can rule out a aging dying compressor with multimeter?
- AUTHOR
Jeff, if you've already cleaned the coils, then there must be an air leak someplace.
Randy
Randy,
Removed the shroud and the cover inside the camper. Squirrel cage was turning fine. With the cover off I could feel more air flow than with the cover on. At this point, i have to assume that this unit just doesn't move that much air. Seems to be cooling fine, temp inside the camper was mid 90s and the air coming out of the vent was 53-58 so nice drop there. Do you know of anything that can be done to increase air flow coming from the blower?
- AUTHOR
Jeff, the squirrel cage fan may be loose on the motor shaft. You'll find out when you remove the shroud. I'd like to know what you find out.
Randy
It isn't a ducted system. It is a Duo Therm Quick Cool by Dometic. The fan motor turns fine, but there is no air flow coming into the camper. I figured next step was to get into the unit and see if the blower wheel was damaged/dirty. Any other tips appreciated. Thanks again for your willingness to help the rest of us!
- AUTHOR
Terry, more than likely a bad thermostat or control board. Check the stat first before replacing the control board.
Randy
1 year old, 24' M.H. always plugged in with surge suppressor, Dometic a/c cools for 2 minutes then blows warm air. tried resetting but does the same thing everytime. Has a touch screen control & aircon module.What might the issue be?
- AUTHOR
erdmannjohn, it's in the unit on top of the camper. Check on Amazon to see what it looks like.
Randy
- AUTHOR
Jeff, if you have a ducted system, you may have some collapsed ducts.
Randy
i am having a problem with my rooftop rv a/c unit that sounds like it could be a bad capacitor I need to know where the capacitor is located. is it in the trailer or on the rooftop unit itself?
Great articles! Thanks for taking the time to write them. My fan motor turns but there is very little air flow out of the vents. And tips on how to increase the flow/where to look for restrictions? Thanks!
- AUTHOR
Charles, yes a weak cap can cause this problem.
Randy
My ac draws down and makes my lights dim for like 10 seconds and then the lights go back to normal , it cools fairly good wondering if this could be a bad capacitoer causeing my lights to dim
- AUTHOR
Kathy, yes if there was a large draw on the aforementioned box, it could have affected the control board in your AC.
Randy
I have a living quarters horse trailer the AC works fine and cools the trailer down but it runs for about a minute on full power then it runs for a few seconds at half power do u know what could cause this? I was pkugged in at a pole where there were a few very large motorshomes also plugged to the same box it was extremely hot and the breaker at the kept tripping could that have damaged my A/C? Just replaced the convertor bc fuses were blowing now everything in the trailer is working fine except ac...thank u
- AUTHOR
Shawn, thanks for reading and let me know if you need advice.
Randy
Great article! My unit is making a heck of a racket/rumbling. I will be removing the rooftop shroud today and see what I can find. Thinking something has come loose. Thanks for all the advice and detailed information.
- AUTHOR
Chuck, may be bad fan motor sleeves. Try oiling them with a light machine oil and this will tell you if it is indeed worn sleeves if the noise stops.
Randy
When unit kicks on it makes a squealing sound and then runs fine. Also same sound when it shuts off. Works fine in between start and stop. Any advice?
I’m testing now, but I believe the fan stops blowing after a while but the compressor doesn’t turn off. It would seem that if the sensor or themostat were bad it would affect the fan as well. I can turn the fan off manually but if I turn the front a/c to the off setting, the compressor doesn’t stop running. Only if I flip the breaker off. When I first replaced the control board, everything worked properly. I flipped the breaker and left it off for about an hour or so. It is cooling now and the fan is blowing but the compressor came on as soon as I flipped the breaker back on, before I turned the a/c on.
- AUTHOR
Chris, hopefully it's simply a bad sensor, but other than that, I'm stumped! I'd be interested to know what you find out about this problem so I can assist others with a similar problem.
Randy
Sorry I didn’t provide better info. The touchscreen I have controls my entire coach pretty much. All the lights, both ac units, furnace, slides, awning, water heater, tank heaters, and vent fans.
- AUTHOR
Chris, I didn't realize you had two units controlled by a touchscreen. Still, something is apparently affecting the control board and there's not much left to replace on the electrical side.
The screen has separate tempsettings for each unit and it's possible there's something screwy going on.
Randy
Thanks for the reply. I’m not sure where the thermostat is located in my coach. I have front and rear units and both are controlled by a touchscreen near the door with sensors in the front and rear areas. If I replace the thermostat, will I need to replace the control board again as well?
- AUTHOR
Chris, this is normally a control board issue, but since you've already replaced it then I suspect a bad thermostat as the issue.
Randy
Randy, I have a Coleman Mach system. Noticed the compressor running but not the fan and it would not turn off with the thermostat switch. Had to flip the breaker. Replaced the control board assuming that the relay was bad. New control board worked for about 2 weeks and now the same issue. No cooling, and the compressor will not shut off unless I flip the breaker. Any ideas?
- AUTHOR
Roy, the stat sends signals to the control board. It could be either but make sure it's not the stat before replacing the control board.
Randy
The stat is horribly inaccurate. For example, I can have it set to 79 degrees and the compressor will not kick off until 71 degrees. This season it seems to have gotten worse by far. I have never checked out the control board. Anything in particular I should know about it?
- AUTHOR
What is the problem, Roy?
Randy
Randy, I have your basic, run of the mill, non digital or programmable Coleman Mach thermostat. I have about a 27' RV about ten years old. Nothing too fancy. The stat has a "Cool-Fan-Off-Heat" setting and a "Low-High-Low-High" Fan setting.
- AUTHOR
Brandon, have the capacitor(s) checked first. Any AC or electric motor repair can check and replace it for you. Cheap and easy to replace in most cases.
Randy
Question.
What if ac was working then turned off for a few hours. Now I only got a single click noise and ac doesnt turn on?
- AUTHOR
Roy, are you sure it's the stat causing the issue? It may be the control board which receives the signals from the stat itself.
Randy
Randy, I have your basic, run of the mill, non digital or programmable Coleman Mach thermostat. I have about a 27' RV about ten years old. Nothing too fancy. The stat has a "Cool-Fan-Off-Heat" setting and a "Low-High-Low-High" Fan setting.
- AUTHOR
Roy, I 'm not sure which stat you need to replace yours with as there are so many different models. Sorry!
Randy
Randy, my Coleman Mac thermostat is buggy and I want to replace it with a programable (digital) and more accurate one. I tried to replace it last summer with a digital Honeywell and learned not all thermostats are created equal, ending up putting the original one back on. Any suggestions on a replacement?
- AUTHOR
Neil, more than likely a bad capacitor. Cheap and easy to replace.
Randy
Randy, Great article! I have had a problem with my Coleman Mach twice now. Turned on the AC, fan runs but the compressor doesn't. After about 30 minutes the first time (last year) the compressor came on and the AC did fine for the rest of the trip. This month upon reaching the park, the same thing happened except the compressor did not start until about 12 hours later. Any Ideas?
- AUTHOR
Brad, the specs on your unit are well within the range for the compressor so apparently there's something else causing the issue. You may be correct in there being an issue with the GFIC.
Randy
Randy -
Here is some information from the Airxcel sticker inside the unit. Let me know if this helps.
Compr. LRA 63.0
Compr. RLA 12.2
Fan Motor FLA 3.4
Minimum Circuit Amperage 18.6
Maximum Overcurrent Protective Device Amperage 30
Minimum Overcurrent Protective Device Amperage 20
Thanks, Brad
- AUTHOR
Brad, what amperage does your unit call for normally? |It should be listed somewhere on the unit near or on the compressor.
Randy
Randy,
Thank you for your response.
I was able to connect to a non-GFCI circuit and ran the compressor 3 times with the following results: start up amps = 22-28 amps, run amps = 7-9 amps. Compressor (A/C) seemed to run fine from this non-GFCI circuit.
I also attempted to run from generator and the compressor would not start. It would draw about 14 amps, then the transfer switch would kick out and begin cycling on/off, trying to start the compressor. What is strange here is that if the compressor is bad, I would think the breaker would kick out instead of the transfer switch.
What are your thoughts on the measurements?
Should I chase anything else?
The only other thing I'm thinking is that I have a ground fault somewhere in the A/C circuit, thus blowing the GFCI and generator is hesitating to connect? If you support this thought, where should I start?
Thanks, Brad
- AUTHOR
Linda, if you have a GEN/SHORE switch, be sure it's working correctly. Otherwise, check the amperage output on the generator.
Randy
Randy, we have a dometic in our new 2019 leisure vans unity motorhome. The air conditioning works when we are plugged in but not when we have the generator on. Same with the microwave.
- AUTHOR
Brad, if you can borrow or rent a clamp on amp meter, you can see if the compressor is drawing more amps than normally required. It will be difficult to do if the power shuts off immediately though.
All things seem to point to the compressor being bad anyway.
Randy
Have a 2012 Coleman Mach 3 A/C unit that appears to have a bad compressor, but I'd like your thoughts.
Here is where I'm at at so far:
- Blower motor works fine in both high and low settings
- Thermostat seems to work fine
- All capacitors (3) tested good
- To be sure, I changed both start and run capacitors for the compressor & no difference
- On shore power: When compressor is actuated by thermostat, GFCI outlet from home 110V triggers and shuts off power to the coach
- On generator: When compressor is actuated by thermostat, transfer switch flips back and forth until generator eventually shuts off
- Resistance reading on the top of the compressor (without wires attached) are: Red to white 5.8 ohms, Red to black 5.2 ohms, and White to black 3.1 ohms
Are there any other tests I can run to be sure its the compressor?
Thanks, Brad
- AUTHOR
Sara, more than likely the mistake burned out the control board in the AC. And the microwave may be toast as well.
Randy
We moved to a new rv park when we left the one we were at to the other rv park we were on a 30 amp spot at old place and when we got to new place the rv got plugged in to a 50 amp plug and ever since then the AC and microwave hasnt work but the heater part of ac unit still works.
- AUTHOR
Mike, when you say you can hear the motor, do you mean the fan motor or the compressor? If it's the compressor running, then you may need a new fan capacitor.
Randy
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