Air Conditioner '89 Caprice R134 converted.

[Lgilder]

I have a 1989 Chevrolet Caprice 9C1 (police). I have a bit of an anomaly with the air conditioner. It began about a month ago. The air conditioner cools great for about 10 min while driving, then it either totally quits cooling and begins blowing warm air or either it begins blowing slightly cool air, but nothing near what it normally can cool. It has been to every self proclaimed pro in town and no one can fix it other than throwing parts at it or trying to convince me to replace the entire system. The high and low pressures have been checked and are normal. It is not low on refrigerant as that has been checked several times. So far the cycle switch for the compressor has been changed and the relay for the blower was replaced. The problem is the cooling ability and the fact that it is intermittent. The compressor and clutch are working correctly. Does anybody have any ideas or suggestions thank you.

[Jsdirt]

I'd check the blend doors for proper operation, and also the foam seals around them. You might be getting air that's bypassing the evaporator altogether, or going through the evaporator & then mixing with the hot heater core.

 

If the system is fully charged, the pressures are good, air blows out of the vents nice and strong, & the lines going into and out of the evaporator are close in temp (or outlet slightly colder), that's the only thing it could be. If the evaporator is cold, air is either bypassing it, or getting heated up. If the high side is spiking, then you need a new fan clutch, or you need to clean debris trapped between the radiator & condenser. If air is a little weak coming out of the vents, you might have a plugged evaporator. Leaves, pine needles, & other organic trash loves to find it's way in there ...

[Doug_Scott]

I would add that once it starts to act up, pull over and do the checks Jsdirt suggests regarding temps of a/c lines. If possible, when it is acting up, run a garden hose over the condenser with the engine idling. That will verify that the air flow is too low(a/c immediately starts blowing cold air) or that air flow is satisfactory(no change in a/c behaviour).

 

The a/c system(hvac box part) usually works on vacuum. If any of the actuators are starting to leak (diaphragm gets dry and cracks) it can be a bitch to locate. But, again, if you can get to it when it is not working correctly you may be able see if the blend door actuator is not fully engaged. Keep in mind though that just because it is not fully engaged, it does not mean the actuator is bad, it could be vacuum supply or something holding the blend door.