If your AC is not cooling like it should, the next step is to find out why. This is where things can get tricky. In order to properly diagnose an AC system problem, you need at the very least a set of AC pressure gauges. At present there are two types: one for R-12 and one for R-134a. Be sure to use the correct gauges for the system you're working on. You don't need to hook up the gauges right away, however, as a good visual inspection can get you started. As stated in the previous section, be sure to check the operation of the AC compressor. The compressor is divided into two parts. One part is the actual compressor and the other part is the compressor clutch assembly.
The compressor clutch assembly engages the compressor when activated. It's an electromagnetic device that, when active, connects the compressor input shaft to the drive belt on the engine. When it’s not active, it allows the compressor pulley to just freewheel. You usually hear a click when the AC compressor clutch engages, and then the front of the pulley starts to spin (or it should start to spin). If this happens, it means your compressor and compressor clutch are capable of working. You might also notice a slight change in the engine idle when the AC compressor clutch engages, this is due to the extra load the AC compressor puts on the engine when it’s active and is perfectly normal. If your engine stalls out when the AC is active there could be an issue with the idle circuit or there could be a problem with the AC system. See the Idle Issues Article for more information on how to solve idle issues.
If you hear a lot of noise when the compressor engages, first check the belt tension. If the belt is loose, it might slip and cause noise. It could also be the compressor clutch or the compressor itself that's making the noise, so be sure to try to nail down the source of the noise if you have one. You can use the information in the Noises article to help you with that diagnosis.
After verifying that the compressor works, the next thing to check for is cooling fan operation. If you have a FWD vehicle, it normally uses electric fans to cool the radiator and condenser. Make sure these are working when the compressor is on. If not, find out what the issue is and go from there. You can get more info in the Electrical article to help you figure out what's going on with your fans.
In addition to making sure the compressor, compressor clutch, and fans work, it's a good idea to look over all the hoses and fittings for the AC system. What you're looking for is any oil residue that might indicate a leak. AC leaks are probably the number-one cause of AC system issues, and a good visual inspection is one way to
find them. Also, look at the front of the condenser. This is the part of the AC system that's placed in front of the radiator. If it's clogged up and blocked with debris, remove it and recheck your AC system performance. Remember, the condenser needs to get rid of heat. If it's blocked off, it can't do that very well and AC performance will be compromised.
There are a lot of things that can cause AC problems. That's really the thing about AC. You can have a problem with leaks, electronic issues, or pressure problems created by a whole host of possible causes. It takes years to develop the skills to properly diagnose an AC system. Honestly, there really isn't enough space for me to get into a complete AC diagnosis, as there is so much to cover.
I get asked about AC problems a lot. If I’m going to make any recommendations here, it's to take your AC issues to a professional. They have the equipment and the know-how to do it correctly. If you're just topping off your system until it gets warm again, you're not addressing the root problem and you're also causing damage to the environment. I consider this irresponsible behavior.
I won't lie; AC work can be expensive, in fact very expensive, but it's a luxury many people can't do without. If you find yourself in this situation, you might consider taking your vehicle to a repair facility to be diagnosed and have the refrigerant recovered. You can then do the work yourself and take your vehicle back to the shop to have them evacuate and recharge the system when you're done. The choice is yours where the law allows. I just urge you to be responsible when working on your AC system.