Auto body repair & detailing: Air Conditioning, vent openings, gmc sierra

Question
Hi Mr. Forster,
The AC expert is unavailable, so I hope you can help.  I have a 1997 GMC Sierra, and the AC just started running cool, but not cold.  A friend told me I can cheaply purchase a kit, and recharge it.  

How?

Thanks,  M.

Answer
Hello! I'll try to help. Is the a/c compressor running constantly when the a/c is on max, or does it frequently cycle off? You will hear the compressor clutch engage, and disengage when you turn the a/c on and off. Listen for the clutch to engage when you turn it on max. It should stay on. If it does not, yes, you can put a can of r134A in with a kit you can purchase at any local auto parts store. I would try to find a 12 ounce can to put in, not the larger cans that have 20 or so ounces. If you only can get a larger can, only put in half of it. Overcharging the system will also keep the system from cooling properly. Now, if the clutch is staying engaged, you could have a vacuume leak. That will affect your heater control board. Cycle the A/C controls, starting with the air flow blowing from the floor. Then, change the controls until it's set to blow through the dash vents. If there is no change, or the change is very slow, you have a vacuum leak in the engine compartment. One of the hoses is either cracked, has come off, or has just plain rotted. If you have a problem with mice in your area, a mouse could have made a nest somewhere in the dash air flow system. A tell tale sign will be bits of seat stuffing on the floor of the truck around the lower vent openings. however, that isn't always going to prove the existence of a nest. Bill