A/C Performance

Since you are not familiar with how A/C works, here some background theory:

The condenser is up front of the radiator, and it is supposed to condense the hot gas from the compressor into a hot liquid. The hot liquid goes to the expansion valve located in the last 6" or so of tubing next to the firewall. The expansion valve lets the hot liquid expand and become a cold gas, the cold gas goes to the evaporator inside the car where the fan blows on the evaporator exterior. The heat transfer from the air inside the car to the cold gas inside the evaporator causes the A/C to blow cold air. The now cool gas goes to the compressor where it gets compressed again into a hot gas and the process starts all over again. Keep in mind that this is a closed system, and the gas inside the A/C doesn't get out unless there is a leak, which is where you are at.

Here's where the problem gets sticky. All the original fox body Mustangs were made to use R12 refrigerant. R12 is no longer available unless you have an EPA 609 license. That means the system needs to be converted to use R134. Putting R134 on top of R12 without doing a proper conversion will cause compressor failure and metal from the compressor will circulate throughout the system. When this happens, it requires an extensive and expensive flush of the A/C system to get all the metal and other contaminants out. Skip doing the flush and clean thing and the new compressor will quickly fail.

When a R134 conversion is done, the installer is supposed to replace the service fittings with R134 style quick connector couplings.






Then he places a R134 conversion sticker on the car. The typical sticker looks like this, yours may be different.



They are also supposed to replace all the O rings with R134 compatible O rings. The R134 gas molecule is smaller than the R12 molecule, so R12 O rings will be prone to leakage.

See R134a Conversion for R134a Conversion & recharge help

If the gas leaks out, usually it is because one of the O ring seals is bad. High quality R134 conversion is supposed to include new green O rings for all the joints and couplings. When you open the system to replace the O rings, all of the refrigerant must be removed and recovered and the system vacuumed down prior to recharging.

R134 recharge kits with refrigerant/leak detector dye can are available at most auto parts stores. Some of the R134 refrigerant refills have a leak stop in them. BUT beware! The stop leak can block the expansion valve, causing system failure. The refrigerant/dye recharge kits are popular because the green dye makes a very visible indicator where the leaks is. Some of the recharge kits include a pressure gauge so you have some idea of how much refrigerant is in the system while it is running.