Yet another A/C problem
 

I'm a good self-taught mechanic but I don't have a repair manual for my gf's 1992 SL2 Saturn. We are going on a long trip soon and the A/C system is not working. Here is whats going on:

-On pressing the AC button, the clutch does not engage but it lights up.
-The following works perfectly:
-All electrical grounds are sound
-All refrigerant lines (hp and lp) are in good condition with no signs of leaks
-The evaporator, condenser, TCV, compressor and reservoir / dryer are in good shape and clean showing no signs of leaks
-I tested the clutch, works just fine.
-I tested the green wire leading from the clutch to the fuse block, right to the relay terminal (#87)
-I tested the horn, cooling fan and A/C relays, all are identical and all test 100%
-I tested the leads on the fuse block and I get +12V to #30 always, +12V to #85 only when the car runs
-I get NO GROUND from terminal #86 when the car is off, running as well as when the A/C button is on.
-I traced terminal #86 from the bottom of the fuse block using a continuity test and determined that #86 connects to an 18 gauge dark blue wire.

I am unsure of where that wire traces to, it seemed like it went to the engine harness but even after testing all the blue wires there, determined that infact they are not my wire.

Anyone know where that blue wire goes so I can continue my testing? I know it grounds out whenever the AC system needs the compressor running but I am unfamiliar with automotive AC systems and I'm not sure if the blue 18 gauge wire goes to a control circuit or directly to the switch. I'm about to go into the dash to check the switch, the indicator light may work but its possible the switch doesn't work or is there another switch to keep the system off in case of low refrigerant?

Anyone have a manual or wiring diagram online? Thanks for any help. BTW: Where is the ECU? Under the fuse block in the wheelwell or something?

Per the Chilton schematic (91-93), the dark blue wire comes off the low side of the inductive part of the A/C control relay in the underhood junction block and goes directly to the PCM A/C Relay input. However, the A/C Request circuit contains (in series) a normally closed A/C high pressure switch, and a Normally Open Held Closed A/C low pressure switch.

I suspect the low pressure switch is open due to low refrigerant level (usually a $0.50 o-ring gone dry) . This will indirectly inhibit the A/C clutch from engaging (that circuit is separate but is also fed from the capacitance low side of the relay) since presumably, the A/C request line must be in the correct state in order to allow closure of the relay. This won't happen if the low pressure switch is open.

Get refrigerant level checked. If you have a leak, you're looking at a conversion to the new refrigerant---this is not a DIY maneuver if you want your compressor to last.....

Please keep us posted.

Oh I believe the PCM is under the dash



I'm there with you on my 95 SC2.

Thanks for the prompt reply. Thats just the info I was looking for.

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