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99 s10 compressor not engaging

Jim Davis on Sun September 04, 2011 3:24 AM User is offline

Year: 1999
Make: Chevrolet
Model: S-10
Engine Size: 2.2
Refrigerant Type: 134A
Ambient Temp: 79
Pressure Low: 73
Pressure High: 80
Country of Origin: United States

On the pressures, these where static pressures, engine on and off. Compressor clutch would not engage. I got this thing from my son in law in a trade, yes, I got the short end, but..... On inspection found one of the prongs on the compressor plug in bent over, straightened it out, now have a good connection, added approx 18 oz of refrigerant just to see if it would kick on. Had to jumper 12v to compressor to engage clutch and add refrigerant. Would blow cold while jumpered, but would kick off as soon as I cut jumper. Pressures while jumpered where low 33-34 and high 199. unhook jumper and back to static pressures of 69 and 75 (low, high). I could find no cut out or pressure switch on the compressor itself, on the backside, and on the pressure switch on the orfice tube line, there is 3 wires. Factory service manual says apply 12 volts here, but not which wire. I know I need to, and will, recover, install new dryer and o tube and recharge, but would like to make sure I am not missing something or there is not another problem with the compressor not coming on when the controls are turned to ac or max ac. Temp controls seem to work fine, heat when on hot, etc. And its late, but I do think I remember when I turn the ac on, the engine surges like its expecting the extra load from the ac. Thanks for any help, Jim.

GM Tech on Sun September 04, 2011 8:49 AM User is offline

You said you got "the short end" truer words may never had been spoken.....

2.2l S-10's were famous for shorted a/c compressor clutch wire agaist the heater pipe approx 6 inches from compressor. Is your red 10 amp a/c fuse blown in electrical/relay center underhood? If so take air intake snorkel off- 10mm bolt and a ring clamp-- then look where it rests on top of heater pipe where a/c wire lays-is the wire bare from wear?



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The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

Edited: Sun September 04, 2011 at 9:33 AM by GM Tech

Jim Davis on Sun September 04, 2011 4:55 PM User is offline

Thanks, checked that and its ok, probed the wiring from the compressor back to the relay and fuse, thats good, ground good, got out the wiring diagrams and now going to start probing back to the pcm, the cycling switch, and I guess back to the control head.

mk378 on Sun September 04, 2011 9:21 PM User is offline

If the engine really does rev up, that shows the PCM is getting the A/C command. The problem must be after the PCM.

GM Tech on Sun September 04, 2011 10:35 PM User is offline

No cycling switch with a variable stroke compressor...you have a 3 wire pressure transducer that feeds the PCM the exact system pressure- then it decides to turn off compressor if pressure is too low (47 or below) or too high (427 or above) ...check the transducer wires one is 5 volt, one is ground, the other should vary between 0 and 5 v olt depending on high side pressure. So at room temp, the voltage should be just under 1 volt or so...

-------------------------
The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

Jim Davis on Mon September 05, 2011 1:52 AM User is offline

Well, I found it, should have looked closer at the start. Wire harness between the underhood fuse/relay box and pcm, harness had sagged and been in contact lightly with the heat shield on the manifold. Didn't really look burned but wire loom was brittle, and bottom few wires where cooked, the green/white stripe from pcm to compressor relay was the only one really damaged. Couldn't get an ohm reading between pcm connector and relay, so started running the wires and found it. AC is ice cold, but have not run it any time. Thanks for the help.

steve325is on Tue September 06, 2011 3:55 PM User is offline

Quote
Originally posted by: GM Tech
No cycling switch with a variable stroke compressor...you have a 3 wire pressure transducer that feeds the PCM the exact system pressure- then it decides to turn off compressor if pressure is too low (47 or below) or too high (427 or above) ...check the transducer wires one is 5 volt, one is ground, the other should vary between 0 and 5 v olt depending on high side pressure. So at room temp, the voltage should be just under 1 volt or so...

Is that one of the "improvements" they made when the switched to the V7 from the V5? The harness on my '94 isn't routed that way.

-- Steve

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