AC Problems
Thread Starter
Team Owner
Joined: Jul 2004
Posts: 28,332
Likes: 3,247
From: Hartford WI
AC Problems
Seems like my AC works, I think. doesn't feel that cool. Maybe it needs a recharge. My main concern is that the air blows out the defrost and on the right side of the driver footwell. Anyone have any ideas where to begin? This is the totally electronic unit on a 91 Coupe
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Air distribution problems are generally related to vacuum. Make sure the source, which comes from the rear of the intake plenum and leads to a check valve just to the left of the distributor is intact. If it's ok, it's usually the Programmer. That's above the accelerator and to the right.
If you have a scanner, the pressure sensor will at least show you what the high pressure is on your a/c system. The ECM will also shutdown the a/c if the pressure is too low and spit out a trouble code; ie, if it was low on gas, the compressor wouldn't be engaging at all. A quick check is to feel the evaporator inlet (at the bottom of the case right where it enters) and outlet (on top). Both should be colder than the ambient air temp with the outlet a tad cooler than the inlet. If the top pipe is sweating or if there's a lot of water coming from the evaporator case, that's another sign that the charge is ok.
Assuming that the charge is good, then the temp door may not be operating properly. It's controlled by an electric motor which gets it's signals from the Programmer (or the same part that controls vacuum to the air doors). To see what the door is doing, remove the blower module on the top left side of the evaporator case and while someone pushes the buttons from 60 to 90, see if the door moves. If it doesn't, the door linkage is connected by a plastic clip to the motor and that sometimes breaks. Otherwise, it's the motor, related wiring or the Programmer.
If you have a scanner, the pressure sensor will at least show you what the high pressure is on your a/c system. The ECM will also shutdown the a/c if the pressure is too low and spit out a trouble code; ie, if it was low on gas, the compressor wouldn't be engaging at all. A quick check is to feel the evaporator inlet (at the bottom of the case right where it enters) and outlet (on top). Both should be colder than the ambient air temp with the outlet a tad cooler than the inlet. If the top pipe is sweating or if there's a lot of water coming from the evaporator case, that's another sign that the charge is ok.
Assuming that the charge is good, then the temp door may not be operating properly. It's controlled by an electric motor which gets it's signals from the Programmer (or the same part that controls vacuum to the air doors). To see what the door is doing, remove the blower module on the top left side of the evaporator case and while someone pushes the buttons from 60 to 90, see if the door moves. If it doesn't, the door linkage is connected by a plastic clip to the motor and that sometimes breaks. Otherwise, it's the motor, related wiring or the Programmer.
Thread Starter
Team Owner
Joined: Jul 2004
Posts: 28,332
Likes: 3,247
From: Hartford WI
I broke down and bought myself a set of GM service manuals with supplement for a 91 Vette. Best $71 I spent. I found the hose from the intake manifold to be disconnected from the hose going to the controller. Saved myself at least $71 for a mechanic to diagnose it. It works now. Will have to check how cool it gets tomorrow when the sun gets up. Might be time for a R134A recharge. Anyone know what amount of R134A they used? TIA
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
About 2 lbs or 80% of the R12 charge which was 2.25 lbs. Without knowing your operating pressures, it's a bit dicey to just dump in some gas. You might want to invest in a manifold gage set first and keep in mind that your Vette's system will shut down if it low on refrigerent.
