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.

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.

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.

• 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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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 coil fin comb to straighten any bent fins because they too will keep the airflow from moving through the AC coils efficiently.

These fin combs are very inexpensive and may be used many times in the future on both RV and home AC coil fins.

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.

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.