I have the same exact scenario you mention. 2010 Cadillac CTS4 Premium 3.6L AWD - bought it used.
No A/C, When A/C or Defrost is turned on - Clutch doesn't engage and hence compressor doesn't spin
Compressor Clutch is OK - clicks when I jump the relay.
Radiator Fan is OK but doesn't turn on - Fan Runs if I jump 30-87 pins on FAN1 and/or FAN2 relay.
On the FAN1 relay as well as A/C compressor relay, when front Defrost is on,
86 to grnd = 3.5vdc
86 to 85=8.5vdc
86 to pos= 8.5vdc
Battery = 14vdc (when engine is running)
So, it seems to me some sensor's input is being taken by ECM to give lesser voltage at 86 of both Fan1 and Compressor - relays. Other relays, I don't see this issue. That tells me that there is some other sensor whose inputs are causing this 3.5v offset - could it be the ambient temperature sensor (ATS), or the evaporator temperature sensor (ETS)? If the (faulted) ETS is sensing very low temperature, then A/C wouldn't kick in.
I jumped A/C relay to force the compressor run for 1 minute - it ran and both the high and low pressure lines were warm - so there is R134a for sure. Radiator Fan was not spinning, so the refrigerant couldn't get cooled enough in the condensor - or may be pressure is low.
Everything else electrical in the vehicle works fine.
BTW, the PCM (or ECM) is under the fuse box - bit hard to unseat the fusebox and reveal the underside of it to see if there is any corrosion - I loosened it a bit and checked out - it seemed good to whatever extent I could see.
Any help?
Joe Wright2 -Did your issue get solved?
Thursday, August 3rd, 2023 AT 11:46 AM