P38 A/C Blows Warm

My A/C blows warm and I occasionally get the little notebook code on the display of my 99 RR.  Last week I inspected all fuses and even swaped a few relays to try and get the compressor clutch to engage.  No Luck there.  Today I verrified the the refrigerant level was correct and the clutch still did not engage.  I have tested for power at the compressor - 0v.  I ohmed the connector to ground and had good continuity.  I started visually inspecting the system and did find the sensor on top of the Drier was unpluged.  I pluged it in and still no engagement.  I unpluged the sensor in the high side line next to the drier and jumped the two terminals together in hopes it would work, Nothing.  I am pretty sure my outside air temp sensor is working correctly cause it has always been pretty accurate with the temp.  I am also pretty sure the inside temp sensor works as I was able to get the fans to change speeds using the cigar lighter test.  I did jump power and ground to the compressor and it will engage and blow cold air.  So what is preventing my compressor from engaging when I have the A/C on?

I am guessing a controller issue or a pressure switch issue.

Any Thoughts?

thread is continued here:
 
http://www.lrrforums.com/showthread.php?t=7141

Im having the exact same problem on my 96 4.0.  New trinary valve, charged system, and nothing, only hot air.  When i run a 12v direct to the compressor, it is ice cold......?????????