First post so, HI everyone. I'm looking for a little help before I start replacing more parts on my 92 1500 w/350. I've searched the forum, but "ac" and "a/c" are too short of words to search for. Anyway, the ac is not engaging. I recently switched from r12 to r34 without replacing anything(i.e. compressor, accumulator, orifice tube.) The system never worked in the last few months I've had it and I thought it was just low on refrigerant. I've checked all the fuses and looked for any relays that may be bad but everything looks good. There is nothing audible in the cabin or engine bay when I hit the a/c switch in the cabin. It seems to me like it is some kind of electrical problem, but maybe I am missing something. Another this is that I can't spin the compressor by hand, which I think you should be able to. I just seems like the compressor doesn't engage or even get a signal to engage... :help:

Pete

The very first thing that I would try: Go to the accumulator that is under the hood and disconnect the pressure switch wire from it. Once the wire is off AND with the A/C switch turned ON, AND the trucks motor is running; jumper the two contacts inside the plug. The A/C compressor clutch should close in and start the compressor turning over.
This is a quick test to see if the problem is associated with the refrigerant charge being LOW. If there is a problem with the clutch not engaging, then further checks will needed for searching for a loss of power. Check fuses first, then 12 volt power into and out of the A/C switch on the dash control. After that I would look at the actual wiring for breaks or a grounded problem.

thanks piecesparts, I just tried the jumper trick and it did nothing. I checked the fuse under the dash for the htr/ac, but that is only for the fan if I'm correct. Is there another fuse for the compressor somewhere that I am missing? I figured that there would be a fuse or a relay for that somewhere. I am going to check the dash switch next to see if that is the culprit. Oh and if it means anything, the "a/c" light is flashing on and off.

According to my shop manual for a 91 truck, the 25 amp fuse under the dash is for (HEATING VENTILATION AND AIR CONDITIONING). ALSO according to my shop manual; the flashing indicator for your A/C is telling you that you have a failure in you electrical system on the Heating A/C control. The book discusses that there are two (2) different flazhing indications to monitor for. The first being the "ACTIVE MODE INDICATOR AND MODE CURSORS", for a Mode error; (My guess that this would be your A/C light flashing, as you said). The second would be "ALL OF THE TEMPERATURE SCALE CURSORS" flashing for a temperature motor error.

The schematic shows that from the CONTROL HEAD (the control panel has wiring that does to an "Air Inlet Motor", wiring that goes to a "Mode Motor", and wiring that goes to a "Temperature Motor". With the indication that you are getting there is a possible problem with the mode selector motor.

The shop manual shows that the MODE ACTUATOR is on the end of the air distribution box, under the dash just above the driver's right foot (gas pedal). The TEMPERATURE ACTUATOR is on top of the air distribution box (about in the middle and just behind where the glove box left end is). There is a short discussion on the replacement of this actuator, if that is the problem.

THERE IS A WARNING IN THE SHOP MANUAL ABOUT CHECKING THE ELECTRICAL CIRCUIT. BE SURE TO NOT USE A METER WITH AN IMPEDANCE OF LESS THAN 10 MEG OHMS. There is also a test for the different actuators that is discussed in this section for each of the actuators, but it is rather lengthy and you may want a shop to do this.

piecesparts, thanks alot for all the help again! I will do what I can with this info and like you said and, keeping the specs of the electrical meter I use in mind, see what I can find. This is definitely a more complex A/C system than I thought. Ultimately, it might be something for a qualified shop to address; I'm more used to the wiring involved in 60s cars and trucks.:o thanks again i appreciate your time

any resolution to this problem? my old man is having the same flashing A/C light on his 92 1500. thanks for any help.

-j-rOd

First thing you need to do is put a gauge set on it and see if it is low on refrigerant.

If it is not low on refrigerant there is a GM SERVICE BULLETIN about this condition.

From the service bulletin:
“The controller monitors the state of the low pressure switch if the compressor has been activated. In addition, it monitors the amount of time the compressor is engaged, if the compressor is engaged for less than 1.5 seconds before disengaging for 10 consecutive cycles, the controller will turn off the compressor, and set a low refrigerant charge condition error, the compressor will not turn back on until the error has been cleared.”
“The digital read out on the controller will flash for a period of 2 minutes and then turn off when this error occurs. It will also flash at every ignition cycle for 2 minutes until the error has been cleared.”

thanks a bunch mang....

Something else to remember is that when converting a R12 system to R134a, you should only charge 80% R134a out of the original R12 charge. How much R134a did you put in? Usually you would pull a vacuum on the system and use that vacuum to pull in the first can of refrigerant. THis should be enough to allow the compressor to cycle then you can bypass the low pressure switch to pull in the remaining charge. I put a single guage on the high side fitting and charge using that. THe proper way would be to use a full blown gauge set and watch both high and low sides. I have seen a lot of people just go buy a extra big "Super Duper Cold" refill can with the hose and gauge already on it and a couple of fittings and think that is all they need for a retrofit. When I do a retrofit, I generally remove the compressor and lines, dump oil from the compressor, replace the dryer, replace the oriface and flush the lines to remove any R12 oil and debris. I will but half of the oil charge in the compressor (making sure to rotate it before installing) and the other half in the dryer if it will take it. Before I start I also pull a vacuum on the system to check for leaks and if any exist I charge the system with about 60-75 psi nitrogen and leak check everything. Leaks are usually the reason for a retrofit. Good Luck

I had this problem in my 91. The mechanic said he just unplugged and cleaned the terminals of my "head unit controller" and that worked for a while. Since he told me what he did, :) I did the same thing every time it quit working again. This happened probably three times last summer and this spring when I went to try my little "trick" again, it didn't work. :( I tool it back to the mechanic and he said the compressor was now bad and so we replaced it and had him retrofit it to 134a. It cost about 700 dollars but it's worth it to ride in the cool!

I should mention too that my 91 (and that poor little compressor for that matter) had 309xxx miles on it at the time of ac failure. Not bad I thought.

…The mechanic said he just unplugged and cleaned the terminals of my "head unit controller" and that worked for a while. Since he told me what he did, I did the same thing every time it quit working again. This happened probably three times last summer and this spring when I went to try my little "trick" again, it didn't work. … Disconnecting power from the control head will clear the “low refrigerant charge error” allowing the system to work again. Disconnecting the battery or pulling fuses is an easier way of clearing the low refrigerant charge error.

309,xxx miles isn’t bad for a compressor