Sunday, June 5, 2011

Feeling Hot, Hot, Hot.......FIX YOUR A/C

Well it is official, I walked outside at 8am this morning and I began to sweat before I reached the mailbox. Alabama is known for great football, paying players, and weather that can make the devil himself search for someplace cooler. And just like clockwork I get all sorts of inquiries and requests for service work on A/C platforms this time of year. I want to cover the fine points of A/C troubleshooting and things you can do to save HUGE dollars.

It is common for people to say "you have to have special tools to do A/C work so you just have to pay what a shop wants to charge". This is pretty far from the truth. I have fixed quite a few A/C units with little more than a $40 gauge and $7 R-134a filler hose. Nope, it ain't fancy, but it works. You simply have to understand the basics of air conditioning and how it works to diagnose and fix your car.

1. Compressor: this is the part everyone automatically thinks is the problem when A/C issues come up. And while they are the "heart" of the system and commonly fail, they aren't always the problem. The compressor moves the refrigerant through the system. It has a high side and a low side. It is turned by the engine and is engaged by a clutch at the front of the compressor housing which engages the compressor. Common symptoms of a bad compressor are:

  • No cold air. If the compressor dies, you are going to be hot.

  • No cold air at idle or sitting still, but gets colder when the engine RPM's go up. Typical sign the suction or low side of the compressor is bad.

  • Horrible noise when the A/C is engaged. Your compressor clutch is bad or going bad, your system might be low on refrigerant and/or oil (yes, there is lubricating oil in the system).

2. Condenser: It looks like a small radiator and is usually mounted in the front of the vehcile. It has small coils and serves to cool compressed air that goes through it and converts to a liquid under pressure. That may make no sense but keep in mind, A/C systems do not "make cold air" they remove heat from hot air and it is a chemical process. The bottom line, the condenser is under great pressures and can and does fail. I have seen holes get knocked in them from road debris, rust through over time, or the seals at the connection points go bad. Usually a leaky condenser is easily seen by injecting UV dye into the system and checking it for leaks with a UV light. You can also buy or rent a "sniffer" which is a tool that detects the R-134a gasses present at the leak site. Most often they are easy to replace and less than $300.

3. Evaporator: This is where the super cool gasses go through and air is passed across it by your blower motor to give you the ice cold air blowing on your face. It looks like a small radiator too and as the refrigerant leaves the evaporator it becomes liquid again. Evaporator problems are sometimes hard to diagnose due to the location. It is almost always behind the dash or firewall and difficult to get to. Labor charges to replace this part are often quite hefty as a result. Here are a couple symptoms to look for:

  • A/C blows cold if you add refrigerant, but it leaks out within a day or two and you can't find a leak anywhere.

  • You hear excessive hissing noises coming from your vents when you turn the car off.

  • You see UV dye around the under panels under your dash where the HVAC system is located.
4. Thermal Expansion Valve (aka Expansion Valve): This is what regulates the A/C temperature if you decide you don't want freezing cold air anymore. It helps regulate the air coming into the car. This little booger has caused more headaches and troubleshooting problems than most of the above parts combined. It just seems to get overlooked. Typically you will get whacky low pressure port readings if this part is bad and you will likely be getting some cold air, but not much. They are usually cheap and easy to replace so that is a positive.

5. Drier: Your compressor only compresses gas, so the drier is there to make sure no liquid makes it to the compressor. It also has a filter in it (some cars have what's called an "orifice tube" which is a small screen filter that is replaceable) that catches crap from the system as well. Not too much can go wrong with this part save for leaks at the connection points. It is a good idea to replace it whenever you open the system for optimum performance. They typically run less than $50.

Those are the main components of any automotive A/C system. Yours may have a few extra parts here or there, but all systems will have the above parts. Keep in mind A/C systems are under immense pressures. If you go loosening bolts on your A/C system and it has refrigerant in it, it will spew out and can be harmful if inhaled. It is also illegal to vent it into the atmosphere. I find that most shops will charge you a nominal fee to evacuate your system for you. Then you can go home and repair or replace parts on your own. All you really need to refill it is a vacuum pump and a manifold gauge kit or you can pay a shop to vacuum it for you before you add R-134a back to the system.

I should note pulling a vacuum is very important and serves a couple functions. Condensation and moisture get into the system when it is "open" so the refrigerant will hit that and freeze causing clogs. Under vacuum water boils at room temperature so the moisture will boil off leaving you with a clean system. A vacuum will also pinpont leaks because if you have one, it won't pull a good vacuum. And finally, after you pull a vacuum, turn the pump off after about 30 minutes and wait to make sure the vacuum holds, this also tells you if you have any leaks. This paves the way for final refilling.

There is no way I can address every concern, but I wanted to give you a few ideas and a synopsis of what is going on so you can make better decisions and even fix this stuff on your own. All auto shops take advantage of people who need A/C because it is a "specialized" area and they charge a premium for it. But if you spend $150 in tools, you can still save hundreds of dollars.

And of course, if you have an A/C problem, you can always contact me and I will do the best I can to help you.

Until next time........."What one man can do another can do!"


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