A/C compressor not pulling in

[mikespain]

Hi all,

1991 tc 3.0 liter

  I have code 33 showing-a/c relay short or open.I tried anothe relay with same connections (85,86 30 87) still not working So I have tested the voltages and grey wire  has 12v all the time,dark blue has12v after  ignition is switced on .Short between gray and dark blue/black compresser clutch engages.with a/c switched onTest between blue orange and dark blue shows 12v but then almost immediately loses earth signal on the blue orange wire from ecu.Any ideas what can cause this?Any help would be much appreciated.

Edited May 20, 2018 by mikespain (see edit history)

[Reaper1]

Does the system have a charge in it? If it system pressure is too low it won't keep the compressor engaged.

[mikespain]

yes there is gas in it,

[mikespain]

Would any body have the pin out data for the engine control module which also controls the a/c from what little information I can see from autozone diagrams.Also the rad fan is running all the time

[mikespain]

Hi again,

where would the ambient temp switch be located?

[Reaper1]

I *think* this is the sensor that's inside the HVAC box used to determine the temperature of the evaporator core to prevent it from icing up. It's a thin, straight piece of metal just kinda shoved in the fins of the evaporator. I *think*. These weren't part of the earlier A/C systems, I think they were introduced in late 89 or 90.