A/C Compressor clutch doesn't engage

[Ed_Strong]

My 1991 3.1L V6 Corsica LT had been sitting for about 3 weeks while I was moving down to Florida. I came back to pick up the car and it fired right up, but when I went to turn the A/C on, I noticed that it wasn't cooling the air. After inspecting the system I noticed that everything is working as it used to with the exception of the compressor clutch that doesn't engage. I checked fuses #8 & #9 and they're good, the A/C control knob cycles normally thru all the settings and I can hear and feel the radiator fan go off when there's an A/C setting selected. The wiring and plug to the compressor also looks good, so I don't have an idea of what could be wrong.
Does anybody have any ideas? I'll be leaving in a couple of weeks and would like to have it fixed.
This is what I've done so far...
I disconnected the wiring plug at the compressor and tested with a test probe and there seems to be no power going thru, So I guess I have a broken connection somewhere. I'm not too good at wiring and electrical stuff, does anyone have the wiring diagram for the A/C system? The wires join up with a whole lot of wires at the coil pack and I don't have the slightest idea were they're routed thru. My Chilton book don't have much to look at either...
I hard wired the Compressor Clutch to the car battery and it engaged. Then I ran the engine and cold air started to come out of the vents. So the A/C system is fully charged and operational. All I need now is some help and a wiring diagram of the A/C system, so I can route the wires to find where the open circuit is and get it fixed ASAP...
Thanks for any help you may provide!

[Kooterskkar]

Does that mean you're not getting power to the clutch? Did you check the relay?

[Ed_Strong]

Originally Posted by Kooterskkar

Does that mean you're not getting power to the clutch? Did you check the relay?

That's right everything works as usuall, but the clutch is not getting any power, unless It's jumpered straight from the battery... What relay are you talking about??? Where is it located? What does it look like?

[richtazz]

the power to the clutch is routed thru the A/C low pressure switch. IF your refrigerant is low, there will be no power there. Check to see if you have enough refrigerant in the system, as they can leak if the car sits for a while.

[Ed_Strong]

As it was stated in the original post the A/C system is fully charged and operational, I did check that out already.
But something odd that happened...
Last nite it started raining and while I was driving back home from work thru the rain I had the A/C on but the clutch would still not engage. As I'm parking the car I hear the clutch engage and it started cooling the air right away... I let run for like 10 minutes and turned the A/C off, then turned it back on without moving the car or anything but the clutch would not engage. I don't know if it had anything to do with the rain or not but that was weird.

[Ed_Strong]

So... does anyone know where does this A/C clutch relay is located at?

[Gooseneck]

Read richtazz's post again, he's on the right track. The low pressure switch could be faulty or your system could be low on refrigerant. The test you made as stated in your original post does not confirm that your system is "fully" charged. And yes rain does have an effect on a/c systems because ambient temperature effects a/c systems.

[Ed_Strong]

Well, right now it's only done it a few times but this is what its doing... it doesn't happen all the time but I've noticed that when the A/C starts cooling (clutch engages), it usually does it after I start the car and turn the A/C on for the first time. If I turn the A/C off leaving the engine running and turn it back on, the clutch won't engage. Mind you this only has happened about 2 or 3 times so I didn't get enought time to diagnose it better.
I don't think the system is low on refrigerant because the times it had worked the air coming out of the vents flows out really nice and cold as it did before and it stays constat meaning the air temp don't fluctuate.
Now how would I go around to troubleshoot the Low Pressure Switch? Is that the one facing up in between the Water Pump and the Radiator on a V6 engine?
Does any one have a picture of the compressor clutch relay, so at least I know what I'm looking for? A electrical diagram would be best but I guess they're hard to get, since nobody has posted on it yet.

[Ed_Strong]

NOTE:
I did the paper clip mode of the ALDL connector and came up with this:

Code 13
Oxygen (O2) Sensor-signal stays low (lean) during warm engine cruise.

Code 62
Gear switch circuit problems
Or
Cruise control problems-vacuum solenoid circuit.

My car don't have Cruise Control by the way...
This codes weren't there before so I don't know if it has anything to do with the A/C clutch problem. I don't notice any driveability problem or difference while driving either. O2 sensor was put in about a 1½ or 2 years ago with a complete engine tune up (plugs, wires, converter etc.)

[Gooseneck]

I'm not sure I know what a 91 Corsica even looks like, so I'm just guessing that the low pressure switch is plumbed into the drier and that the drier is mounted close to the firewall. If you trace the low pressure line (larger line) from the compressor it should lead to the drier. Without connecting gauges to the system, the best way to test the low pressure switch is to just replace it. Around $12.00 at local parts store. I have also been told by a competent source that you can "tap" on the switch and see if this will cause the compressor clutch to engage. If you know anyone in the A/C business, doesn't have to be automotive, commercial, residential any A/C person will do. They can connect gauges and tell you the problem in less than 60 seconds. If you happen to have a can of r134a refrigerant in your pocket, and it is low, he can solve your troubles in 60 seconds more. If you go to your local parts store and tell them you need the low pressure switch for your a/c system, they can show you were it's located on you vehicle. If you can get your hands to it, it's easy to replace, unplug wires, unscrew old, screw in new, plug in wires.

[Ed_Strong]

OK, today I drove around in circles form auto part to auto part stores looking for the low pressure switch and no one carries it. I also asked about the clutch relay, but AutoZone had too many options on their terminal (1.green, 2.red, 3.one wire, 4.two wires). Since I don't even know where the thing is or what it looks like, I couldn't tell the guy which one I needed. Advance AutoParts has one but has to be ordered, it'll be here tomorrow. I tried tapping the low pressure switch like you said but it didn't help.

[Gooseneck]

I don't think the relay is your problem. Once the a/c switch is turned on the relay closes and stays closed untill you turn the a/c switch off. I don't think the relay would cause an intermitent problem. If your low pressure switch is o.k. then I thank your system is just a little low on refrigerant. I know it cools when the clutch engages, it's not out of refrigerant it just does not have enough charge in the system to keep the low pressure switch closed. When you increase the RPM of the compressor the suction side of the system will drop PSI, if the system is low it will drop enough to open the low pressure switch, stopping current to the compressor clutch and protecting the compressor. You need to connect the gauges, come-on, you can shake a tree and a/c men will fall out, you can find one.

[Kooterskkar]

The accumulator/filter drier on a 91 corsica is under the air filter housing, or at least it should be. That's where mine is, it's an '89 but its got the same engine. Ive had a similar problem to this since I tried to recharge the system on mine. It charged just fine and it ran cold as ice for a week or so. Then the clutch wouldnt engage for some reason, and if it did it would be on off on off at about ten second intervals at idle. For ten seconds I would have freezer air, then for ten seconds it would be like a heater. If I kicked the idle up to about 1500 rpm it would stay on, and it would be like a freezer again.

[Ed_Strong]

Well, here it is again... I went ahead and evacuated the system and recharged it with r134 with the proper amount of freon (36oz x 0.80 = 28.8oz). I had to hard wire the compressor clutch again since the system would not engage the clutch. After the right amount of freon was put in and the system was cooling the air to my satisfaction, I turned off the car plugged the compressor clutch harness back in and gave it another shot to no avail.
I've been told that I don't have any low and high pressure switches, just one "pressure transducer" that controls the system by reading both high and low pressures of the line. I can see it sitting right next to the high side port. I traced both lines and can't find any other switches throughout. I also switched the clutch relay with the others next to it to no avail as well. I searched online for info but nothing turn up. Does any one have any other info on how to test the pressure transducer and the clutch relay (jumping wires, meassuring continuity or volts, anything)?

[Ed_Strong]

Success... YES!!!
Oh yeah...
I went to the chevy dealer today and requested the "Refrigerant Pressure Sensor" as it's called on this system and they found it! It's not cheap tho, $55.79 and it was back ordered. So, I went to an independent AutoParts store and gave them the AC Delco part number 15-72104 and they were able to find an after market match for $48. I took a bite at the bullet and went for it, installed it right there in the parking lot and bingo, the AC started working again... Thanks to all that help!
I just regret having to retrofit my AC System for no reason, I hope the change to R134 don't give me any troubles in the future. I doesn't start cooling immediately as it did with R12 and even tho the air is cold it doesn't come out freezing cold as it used to before... BUMMER