Problem: Air conditioner doesn't cool
Automotive air conditioners usually cost a bundle to have them repaired. It takes special training, equipment and parts to do the job right. Because of the high cost of repairs, many people decide not to have the repairs done. They suffer in the heat and start thinking about trading in their clunker.
Many car air conditioner repairs can be done by the do-it-yourselfer, giving fresh life to their car.
The simplest repair is replacing a broken or slipping compressor drive belt, so start with an inspection and/or adjustment of the belt.
Next, check your refrigerant charge and add refrigerant if needed. You'll need an auto air conditioner pressure gage and a refill kit. You'll need to determine if your system uses the older R12 or the newer R134 refrigerant (look for a label under the hood). You must wear goggles when adding refrigerant to avoid being blinded if refrigerant gets in your eyes. If your air conditioner is one of the newer R134 systems, you're in luck.
See if your air conditioner clutch engages and turns the compressor with the AC on and the engine running. If not, or if it cycles on briefly, then back off, the refrigerant charge may be low. Attach the pressure gage to the high-pressure line and monitor the pressure. If the AC clutch never engages, you may have to hotwire the clutch directly from the battery to make it engage. Once the clutch engages, see if the high pressure reaches the factory recommended value. If not, add refrigerant to the low pressure fitting, until the factory recommended pressure is achieved (or about 80% of that for R12 systems retrofitted to R134).
You can buy R134 in small cans at your local auto store, but you can't buy R12. If your system uses R12 and needs a charge, get out you checkbook and go over to the repair shop, since professional shops can still get R12 (it costs a small fortune). Before adding R12, the shop will probably insist on finding and repairing any leaks, adding to the costs.
If you have the older R12 system, you might want to consider converting to R134. A repair shop can do this (bring your banker along) or you can take a chance a do it yourself. Inexpensive retrofit kits are now available at your local auto parts store. The kits include high and low-pressure Schrader valve adapters (because R12 and R134 fittings are different), a can of a special R134-compatible oil charge, a refilling hose, and a couple cans of R134. Be sure you have a high-pressure gage that connects to the new R134 fittings. Remove the old R12. Be responsible and go over to the auto air conditioning shop to have the R12 removed, so as to not contribute to damage to the earth's ozone layer and get in trouble with the law. Follow the kit's instructions and install the R134 retrofit fittings on the existing R12 Schrader valves ... then add the oil charge and the R134 charge up to the kit's recommended pressure. Don't expect a retrofit to freeze you out. R134 is not as good a refrigerant as R12, but it will do the job if the rest of the system is working OK. Also, professionals will probably advise you not to conduct this simple retrofit, insisting that you'll risk damaging your system with incompatible compressor oils. So you be the judge ... pay their lofty price for a professional retrofit or do it yourself for next to nothing and risk a blotched job. If your AC doesn't work, and you can't afford to pay for a professional retrofit, and you can't take the heat, ask yourself if you have much to loose trying the retrofit. Ask around and you'll probably find people that got away with the do-it-yourself retrofit and are pleased with the results.
If you have a seized compressor or compressor clutch, and have some experience working with automotive air conditioning systems, go ahead and replace the compressor with a quality rebuilt unit (in some systems, it's best to replace the compressor and clutch as an assembly). Again, have the refrigerant professionally removed. Make every attempt possible to avoid having much air enter the system. Air does not compress easily and carries moisture. Both are a big problem. The moisture will condense inside the system and combine with refrigerant to create a corrosive acid that damages components. Air can overload the compressor and damage it. Any air and moisture that gets into the system must be drawn out with a vacuum pump before adding fresh refrigerant. So have a suitable vacuum pump ready or don't attempt the job. It is also advisable to replace the drier in your AC system. It's purpose is to capture any moister you missed with the vacuum pump.