Wrench Wench has been in love with automotive mechanics for decades. She loves sharing advice with fellow DIY mechs and curious cats.
Is Your Heater Switch on the Fritz?
There are many possible reasons why your heater has stopped blowing hot air or is acting very peculiarly. The list of things that could be potentially causing only cold air to come out of your car's vents is somewhat long—long enough that there's a definite need to do some initial searching before going much further. Something even as simple as double checking your coolant level can go a long way in ensuring your lack or overabundance of heat is not due to a much more pressing concern—like a blown head gasket or bad heater core.
You'll want to make sure it's nothing big. A bad heater core, bad radiator, or a leak in one of your coolant hoses can become all-consuming problems if left unchecked for even a little while. Smaller challenges, like losing your thermostat or water pump, can also cause bigger problems if not caught in time.
So before we go too much further, make sure to:
- check your coolant level and mixture
- and look for obvious or less-than-obvious leaks in your coolant system.
If you're positive your coolant is full, and there are no coolant leaks anywhere, you're probably pretty safe in assuming there isn't some large and concerning problem in your cooling system.
Next on the list of things that could be causing your cabin comfort woes are the following:
- your heater's blower motor, fan, switches, or fuses
- an accessory belt
- a linkage
- an electronic sensor
If you know how to test your heating system components, or you have someone around you who does, this is a good time to have them do a few quick checks on the motor, fan, fuses, and any sensors.
But if you don't have a friend or family member to test these parts out for you, and you don't the time or experience to do it yourself right now, there are still things you can do to investigate a heater system on the fritz.
Your sacrifices will not be in vain, as they could help explain the source of the problem, especially if the problem has persisted for a little while.
Read on to learn about the three most likely signs that your heater switch is on the fritz and causing your car's heater problems.
1. Wiggling It Makes It Work
Give that switch a wiggle, or a strong jiggle.
Does your heater work properly again?
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Or if you use every mechanics favorite tool—tapping or slapping the side of the dash or the controls themselves—does that bring back your heaters good behavior?
If any of these not-so-great-for-your-car tricks gets your heater back to proper function, this is a big indication that it's your heater switch that's on the fritz and causing your current cabin temp woes.
This symptom reveals the aging weaknesses in the resistor that usually makes all the magic happen. When that resistor gets old, it will lose its ability to resist or stop resisting at various connection points. Almost like it forgets its job from time to tim, like any senior would. And of course, as time goes on, it will continue to have those inconvenient senior moments until it just gives up altogether.
2. Intermittent Airflow
On or off, that's it. No in-between.
No gently warm breeze wafting onto your cheeks.
Your car heater is either cranked to the max, or it's off. Any selection under maximum fan speed pushes out nothing, or barely anything anyways.
Except for just when you've gotten used to it acting that way, and then one day, you leave it on level 2 or 3, and then it suddenly starts blowing at a level 2 or 3, just as it should be.
Intermittent fan velocity is another good indication that your heater switch is on the fritz. It's even more of a positive sign that this is the cause of your cars cantankerous behavior than inappropriate temperature changes.
The reason for this is fairly obvious. If your heater switch is older and starting to feel it's age, their are many components that can be wearing out and losing the strong connections they once had. This can create a break in one of several circuits or mechanical processes that show up as time marches on. The more these parts wear down, the less connections they make, and the more often your car's heating system acts up.
Heater components, especially, seem to have more intermittent-type patterns than other systems, at least in my own experience. Everything from mostly mechanical old jeep heating systems, up to newer mostly electrical Saturn and Pontiac heating systems—they all have had heater switches that went out and had several very peculiar intermittent problems that sent me scurrying throughout the entire cooling system trying to make sure there wasn't a larger problem at stake. They remind me a lot of loose battery connections in that way; they can cause various symptoms that appear to have nothing to do with the source of the problem, at least at first glance.
Note: Air flow problems can also be an indication that your blower fan has gone kaput. If it turns out that your resistor switch is fine, check the fan next.
3. Your Switch Needs a 'Time Out'
If you find that your heater seems to work fine for a while, then stops working or working as strongly, but then comes back full force after being off and allowed to cool down for a while; this can be evidence that your heater switch is wearing out.
This symptom also reveals a dysfunctional resistor switch. As you car travels with you through time, it stops being able to handle the heat that resistors often naturally generate while in operation. When this happens, the switch can get hotter than it's mean to, which tires it out, and can cause it to go temporarily awol. After an often brief cool down period, it will spring back to life like nothing was ever wrong in the first place, only to go out again when it gets too hot.
Whether you've been experiencing the above signs, or you've deduced that your heater switch is bad from other symptoms or sources, the next step is to test your resistor and confirm your diagnosis.
Testing your heater switch is fairly simple, and only requires a few quick checks from an ohm meter. Though because each vehicle may have different-sized resistors, there's no way for me to list a generic ohm frequency to indicate a working or malfunctioning heater resistor switch. I can, however, provide you with a few handy YouTube videos from others who have been where you are now and came out with a fully functioning heater. So for this test, the only existentially difficult work will be looking up the particular resistor used in your specific car or truck.
Even physically, testing your resistor switch isn't all that tall of a task, even for a novice, though that won't make it a total cakewalk for every vehicle owner.
What You'll Likely Need:
- Ohm Meter
- Philips Screwdriver
- Flat Tip Screwdriver
Finding the Resistor Switch
For the most part, the big trick is simply in locating your heater's resistor switch. In most cars and trucks, the resistor is going to be located in the vicinity of the heater interface or nearest to the blower motor. I definitely recommend locating your blower motor first, and following the wires from there. In most cases, if the resistor is nearest to the heater motor, you'll either find it within direct reach, or you'll be able to see it with a flashlight and some unnamed yoga poses.
If you're not familiar with what your blower motor looks like or where it's located, your best bet is to check out a Chilton's manual, or an online guide. In most cases, the blower motor will be under your hood along the engine's firewall, or it will be behind the glove box.
If you cannot seem to find the resistor switch anywhere near the blower motor, then you'll want to check behind the panel that holds the heater knobs. This will require that you remove the interface panel. Depending on how much of your dash needs to be removed in order to get that panel out and look behind it, will determine the level of ease in doing so. Either way, once you've got the panel out, you should be able to see the resistor within a short distance from there. Just follow the wires.
Once you find the resistor, get your ohm meter on it and test for the proper ohms you looked up earlier.
NOTE: In some vehicles, the heater resistor switch can actually be included as a part of the blower motor unit. If this is the case, and it is the source of your heater troubles, then your best bet will be to just get a whole new unit. Unless of course you're in for the adventure of rebuilding your heater blower unit, or having it rebuilt. Definitely not my favorite winter time project, but also not the silliest thing anyone has ever done.
How to Check Your Heater Switch Resistor
Fix That Switch!
Once you've tested and successfully diagnosed a failing or failed heater switch, the next step is to get that resistor replaced as soon as humanly possible. The sooner you allow it to go on malfunctioning, the closer it will get to giving out completely. Once it gets there, or if it's already there, you'll find it harder and harder to comfortably travel. This is especially true if you start having trouble before or during winter months, when being without your heater can actually put your health at risk, even if you're all bundled up.
I know it seems like a simple inconvenience or problem that can be put off for later days when your funds are more abundant, though unless you have multiple vehicles or other modes of transportation with heat, you won't want to wait to get that heater fixed.
In Case of Icemergency . . .
I'm not the first person to have driven a car in the harshest of cold weather moments, nor will I be the last. Though what I've learned from those experiences, can hopefully save a few readers the same bone-chilling experiences.
When it comes to cold-type emergencies you can experience in your car, it's important to be as prepared as you possibly can be. This is especially true if you're having heater problems during the cold weather months, when having to deal with potentially extreme drops in temperature can actually be a risk to your health. Thankfully, there are some easy to acquire items you can keep in your car that are helpful whether your heater goes out, as well as for other emergencies that might leave you out in the cold.
Cold Weather Emergency Kit
|Need to Have||Nice to Have|
Hand Warmer Packets
Car Heater Blanket
Fleece or Wool Blanket
Gallon of Water
Compact Sleeping Bag
Extra Winter Coat
Please Share Your Comments and Stories
As always, please leave any questions or comments below, as well as any additions or refutations to the information I've written. There are so many experiences out there, and so many experienced mechanics, that I often find nothing can be hurt by sharing even more experiences, lessons, or know-how.
Also, I absolutely LOVE to hear your personal stories. So if you've got a story about having to drive around with a heater switch on the fritz, having to test or change one, or getting stuck in a cold weather emergency in your van, please DO share.
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.
© 2016 Wrench Wench