2009 Jeep Grand Cherokee A/C Clutch Circuit Problem

Howdy Group, 

I have a recently purchased 2009 Jeep Grand Cherokee with what I believe to be a PCM control circuit issue on the Air Conditioning.
The AC did not work when I bought it.  (AC schematic attached)

At the A/C clutch relay, I have 12 VDC at pin 30 on the load side.  I had 0 VDC at pin 86 on the control side although Fuse 24 is good.  Between Fuse 24 and the clutch relay is a splice group (S106) that also feeds 12 VDC to a couple of other relays.  One of those relays is the Fuel Pump relay located immediately adjacent to the A/C relay.  Since the engine runs, I concluded that power from fuse 24 through the S106 splice group to the Fuel Pump relay is good, and therefore I have an open circuit from the S106 splice group to the A/C relay.  

It seemed like a much easier fix to tap 12 VDC from the Fuel Pump relay control than to dig into a 1" thick wire harness looking for a broken wire.  So I ran a splice to the A/C relay from the Fuel Pump relay and the compressor kicked right on.  The A/C works great, blows cold.  Physically, the system seems to be good.  

However, the clutch now will not turn off.  It seems that the circuit is supposed to be controlled by the PCM from pin 85 at the A/C relay.  I don't believe that my splice to provide 12 VDC to the relay at pin 86 is the problem, as I believe that there is always supposed to be 12 VDC there anyway.  

That leaves me with a couple of questions...

1. Is the PCM faulty and providing a permanent ground when it should not?
2. Could a fault be with an input to the PCM, i.e.--the A/C low temperature sensor or a low pressure sensor?  

Thank you for taking my question!

Ted 
(SnowmanTX)

SnowmanTX wrote:

That leaves me with a couple of questions...

1. Is the PCM faulty and providing a permanent ground when it should not?
2. Could a fault be with an input to the PCM, i.e.--the A/C low temperature sensor or a low pressure sensor?

1. Before condemning the PCM, verify that the Control wire from the PCM to the Relay is not shorted to ground. Remove the relay from the socket. Then, using an Ohm meter or test light, check the control wire for a short to ground. If ground is detected, snip the wire close to the PCM and test again.

2. The only input that would keep the compressor running is the AC "ON" (snowflake) button, or defrost mode. Other inputs could prevent operation, but I don't see how they could prevent shut-off.

Thank you Chad!

Chad, Thanks for your response. I travel for work so I haven't been home to continue my troubleshooting. In the meantime, I'm watching endless hours of ScannerDanner videos on YouTube.

I'll reply with my findings. While watching all these videos, my mind keeps going back to another vehicle issue that has me stumped. I'll make a new post for that one.

Thanks again!