Solving Automotive HVAC Problems

Blower Motor Problems

The blower motor is really the heart of the HVAC system. Without it, you don’t have airflow in the system. If your blower motor goes out, you won’t have heat or AC. So if you turn on your HVAC and you don’t hear anything, you might start by checking out the blower motor operation. Blower motor circuits are often similar in design. You have the motor itself, a switch to run it, and some form of resistor or transistor assembly that controls the blower speed. If you study the problem, it can tell you a lot about what might be wrong. When the blower is on high, it’s getting full battery voltage so it can run at full speed. If you select some other speed, the current flows through a resistor or transistor assembly that takes away some of the feed voltage. If the blower receives less voltage, it will run slower.

With this in mind, if your blower only works on high speed, what do you think the problem might be? That’s right: the blower resistor or transistor. It’s a common problem and many times is easy to fix. The transistor or resistor assembly is often mounted in the HVAC system and is accessible from the outside. If the blower doesn’t work at all, try tapping the outside of it with the palm of your hand. This might cause the motor to start working. If this is the case, you likely have a bad blower motor or a loose connection somewhere. My money is on a bad blower motor; they do wear out from time to time. It’s a good idea to check for power and ground at the motor first before you replace it. It could be some other issue that causes it not to work, as you’ll see in this video.

Noisy Blower Motor

Sometimes during blower motor operation you might hear excessive noise. Sometimes this noise is not due to a blower motor problem but occurs because debris is caught inside the blower assembly. During blower operation, this debris causes the blower motor to be noisy. This debris often works its way down into the HVAC system from the vent opening under your windshield wipers at the base of your windshield. With that in mind, try to keep this area free of leaves and debris. This will help prevent something like this from happening.

Another cause is rodent infestation. For some reason, mice like the insulation in the HVAC system. They get in there and make a nice little nest inside your blower motor. I’ve even found dead mice in blower motors that have caused this issue. The fix is the same no matter what the cause. Remove the blower motor, clean out the debris, reinstall it, then recheck for the noise. It’s very effective and just costs you a bit of time. Here’s a video on the process.

Cabin Air Filters

Since about 2000, I’ve seen cabin air filters pop up in just about everything. This is a good thing. They help prevent debris from getting into the HVAC, and they help prevent allergens and smaller particles from entering the passenger compartment. I mention them because they are a serviceable item and should be changed out periodically. Every manufacturer has their own interval, so be sure to consult with your service manual or owner’s manual to find out what yours is. A good rule of thumb on these is to change them every 30K miles. You might be surprised at how easy it is to replace one of these. Yes, I have seen some that require way more work than they should, but the majority of them are pretty easy to swap out. Changing your own cabin air filter can save you a lot of money, so consider doing it yourself if you’re due for a replacement. Also, if you haven’t replaced yours in some time, it can cause issues with airflow in your HVAC. If you’re not feeling the air come out of your HVAC vents like it used to, you might want to check the condition of your cabin air filters if equipped. Here’s a video of a typical replacement.

BTW, some filters are located in the engine compartment in the area below the windshield wipers. Consult your service manual to find out where yours is located and how you can replace it.

Defogging Windows

This might seem elementary, but here’s a quick tip to defrost your windows faster. Most vehicles do this automatically, but some don’t. When you have your defroster on, turn on your AC. Doesn’t matter if it’s cold outside; if it’s too cold, your AC won’t turn on anyway. However, if the temperatures are correct and the AC activates, you can speed your defrosting time by turning on the AC with the defroster. This dehumidifies the air before it comes out of the vents, and as a result defrosts the window quicker. With the automatic systems, the AC should come on whenever you turn on the defroster. This means if you have idle issues or perhaps a belt noise when you turn on the defroster, it’s likely an issue with the AC and should be checked out. Here’s a video on this topic.

Summary

Problems with your HVAC will not usually stop you from getting where you’re going, but they can affect driver comfort. In my time as a technician, I’ve found that some people consider driver comfort above all else. This might not be the best approach. Case in point: Person X has an AC problem and wants it fixed. In the process of checking out the AC, we find a major problem with the engine that should be addressed. Person X is only interested in getting the AC fixed because they only have money for one fix. I fix the AC, and they go away for about a week. Then they end up back at the shop with a blown engine. This is an extreme example, but, sadly, not far off from what I’ve seen.

AC work can be involved and expensive, but never forget it’s a luxury item. Don’t compromise the rest of your vehicle because rolling down a window isn’t good enough. Use common sense. Lastly, if you’re going to do your own AC work, do it responsibly. Don’t vent refrigerant into the atmosphere and make sure you have the proper equipment when doing the work.

I hope this information was useful to you. If you didn’t find what you were looking for, type in a few key words into the search at the bottom of the page. You can even type in specific check engine light codes. In addition to the code meaning you may find articles and forum posts that pertain to that code. If nothing comes up for your issue, sign up for our forum and ask your question there.We’ll be happy to help if we can. It’s free, all you need is a valid email address. Just be sure to respond to the conformation email to complete your registration. If you don’t see the

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Stay Dirty!

ETCG

Written By EricTheCarGuy
Edited By Julie Hucke

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