Working on a '98 Trans Am and when I turn on the a/c there's no cool air. Without looking at the compressor I assume it's low on freon and I take it to a friend who is a certified mechanic and has all of the proper tools to recharge it. He checks it, vacuums it, and recharges it. Then when we try it out with a fresh nearly full freon charge (he ran out of freon) and we realize that the compressor clutch is not engaging. He pulls out his electrical test tool and is able to engage the compressor clutch and we have cool air. He unplugs the pressure sensor and the fans go off. Plugs it back in and the fans come back on. Correct me if I'm wrong, but that means the pressure switch is doing what it should, right? It's receiving the A/C request and turning on the fans for the extra work load it will need to cool provided the pressure is within the safe operating range. I also jumped the pressure sensor today (red wire to gray wire) with the same result. Then I try switching in a relay from the horn (which I know works) to test the a/c compressor relay and get no change. Still won't engage the compressor clutch. I'm thinking one of two possibilities: 1) freon is still too low to allow the compressor to run and I need to know how to jump the relay to see if maybe that's it. I don't know what the pressure readings were when he recharged it, but I may be able to find out if he remembers. My 1st question-how do I jump the LS1 relay? 2) Perhaps my hvac control inside the car isn't sending the signal. How can I test that? The car is not modded to death either. Has an SLP lid with K&N filter, an LS6 MAF according to prev owner, EGR stuff has been gutted (throwing egr ses codes until I reprogram it) and the cats were hacked off at the y pipe and a bullet muffler slapped on the y pipe. That's it. Oh, and no a/c codes. Thanks for any and all help.

 

Could be low since you said he ran out. Ask him if he remembers the static pressure (comp off and engine not running). Without looking at my PT chart in helms and assuming at least 85 degrees ambient, guessing pressure should be close to 100 PSIG minimum before fine tuning the charge.

 

Checking with him now. Thanks.

 

He doesn't remember what the static pressure was, but he says there was more than enough for the compressor to turn on. I will have to get the gauges back on it and see where we are. It will probably be this weekend before we can get together though. I'll post up when I get the info. Thanks.

 

Try resetting the pcm. On my car and as far as I know all LT1's if the freon gets too low the pcm will stop engaging the compressor clutch. Then to get the a/c to work you have to reset the pcm. Since he was able to engage the clutch with the scan tool he may have already reset it but it won't hurt to try. Just remove the pcm fuse for a few seconds or unhook the battery.

 

Can't hurt to try......thank you.

 

Well tried the old disconnect the battery to reset the computer trick. No luck. Any other ideas? Thanks again to all who have responded.

 

Well went to the junk yard and lucked on to a car with the HVAC control switch on the dash. Switched them out and still no A/C. Started trying to trace wiring from A/C compressor back since I can't think of anything else to do at this point and found this:

https://www.camaroz28.com/forums/pic...pictureid=4094

Not sure if these wires should be bridged like that because I haven't ever seen one. I removed the bridge and tried the A/C.....still no love. So at this point I know my compressor works, my low pressure switch seems to be performing as it should, the relay is good, the fuse is good, the HVAC switch on the dash is good. Anybody know what else could be keeping the system from coming on? Thanks.

 

I finally got back over to my friends house yesterday and we discovered two problems: 1) there is definitely a leak in my system, as there was almost nothing left in it. Good thing he put some dye in it. Will get to hunting for my leak in the next few days. 2) We discovered that my IAT sensor was reading -34 degrees. So obviously the computer is thinking "It's -34 out dude, why on earth would you want to turn on the A/C? Just roll the window down." Anyways, I'll start working on these two issues and post up when I find out more.

 

subscribing, i have having a very similar prob in my 96z
matt

 

did you try jumping the compressor at the relay. I think pins 30 and 87 should be jumped.
matt

 

Wondering why the IAT is reading so low. It doesn't have one of those old SLP timing trickers plugged in between the harness and IAT sensor does it?