Solving Automotive HVAC Problems

Retrofitting AC Systems

If you have an old R12 system and want to upgrade it to R134a, kits are available to do this. R12 is very expensive if you can find it. Admittedly, it works better than R134a, but given the expense and the potential environmental damage with using R12, it makes sense to retrofit your old system.

You might be surprised at what comes in a retrofit kit: Usually, it’s a couple of fittings and a can of oil. As stated earlier, it’s not a good idea to mix refrigerant oils. The ideal situation is to evacuate the system and remove all the old oil before adding new oil. This will be impossible without the correct equipment. Once you’ve done that, you can then add the new oil in the correct amount and install the new fittings. But beware of these fittings. They often leak.

The takeaway here is that if you have an R12 system, it’s a good idea to convert it to R134a; just be aware of the potential for leaks and the recommendation of changing out the refrigerant oil.

Rear AC Systems

If you have a vehicle equipped with rear AC (SUVs and minivans often are), you need to take special consideration. These systems usually run a separate evaporator and expansion valve in the rear of the vehicle. This means there are lines that run all the way to the rear of the vehicle along with an extra set of HVAC controls to work them properly. If you’re looking for the cause of a problem, be sure to check under the vehicle at the lines going to the rear, and also check the operation of the rear components. These systems often have a separate set of controls and might have their own blower motor as well. The best advice I can give is to not forget about these rear HVAC systems, especially if you have a van or SUV. You might also need to treat them as stand-alone systems when doing your diagnosis. If you have a service manual for your vehicle, this will be very helpful in your diagnosis.

Evaporator Odor

With some older systems built before cabin air filters were standard, you might experience a foul odor coming from the HVAC vents. This is often due to mold and bacteria growing on the evaporator assembly. Think about it: The evaporator is in a cool, dark place and is often covered with moisture. It’s a good place for bacteria and stuff to grow: stuff that can cause odors.

The best fix for this is to remove the evaporator and clean it with soapy water. This is an expensive and time-consuming process, to be sure, but it is the best way I’ve found to deal with the problem. However, there are products that can sometimes solve this problem without requiring the removal of the evaporator. These products are sprayed into the air ducts and ideally work their way down to the evaporator, where they can clean off the offending mold and bacteria. This is often a pretty good fix and is easily repeatable.

One way to help prevent the bacteria from taking hold in the first place is to run the blower motor with the AC off for the last five minutes or so of your drive. This will help dry the condensation on the outside of the evaporator and prevent bacteria from growing there in the first place. If you run the heat for a little bit, it’s even more effective, although a bit uncomfortable in the summer.

Stop-Leak in Your AC System

I’m sure this question will come up at some point. My opinion: Don’t use it. Think about it. I just went through the description of how the AC system works. You take a high-pressure liquid and run it through a small orifice to create a change in pressure and temperature. If you goop that opening up or any of the other small passages in the AC system, you’re asking for trouble.

There are no easy fixes with AC. You can’t use a Band-Aid when you need surgery. Fix it right, or take it to a professional. It’s not likely you’ll fix your AC system with stop-leak products. In fact, I believe you run the risk of permanently damaging your AC system. If you do decide to try stop leak in your AC system, make sure you follow the instructions to the letter for best results.

Black Death

This is the name we use for AC systems that are filled with a black icky substance. As the name implies, it pretty much spells the end of your AC system. I believe this is the result of the rubber AC hoses coming apart internally. Honestly, I’m not sure what causes this, but whenever I see it, it pretty much means the end of the AC system for that vehicle. Everything will need to be replaced: the compressor, the hoses, the evaporator, the expansion valve, the condenser, and the receiver dryer. Once this stuff sets in, it never goes away. Complete replacement of all the AC components is the only thing I’ve seen cure this issue.

Flushing the AC System

If you have a compressor failure, it’s a great idea to flush the AC system out before installing your new one. Many times when a compressor fails it sends small metal particles throughout the AC system. These particles clog up the small passages in the system and cause problems after you’ve replaced the failed compressor. In fact, you run the risk of damaging your new compressor with these small metal particles. For that reason you should always flush the AC system with a special cleaner whenever you replace a failed compressor. It’s also a good idea to replace the orifice tube or screen when you have a compressor failure. Some new compressors come with these parts in a kit.

In summary, anytime you have an AC system that’s been contaminated, you should flush it out before putting it back into service.

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