Need AC system help

The high pressure switch should only be to kick the fan. Unless you've got 2 of them, the other would be to shut the compressor off. 2 is rare though.

Your low pressure is too high also. 28 - 37 is ideal with 34 - 35 being the sweet spot. High should be 140 with fan running. This is with a 1200 rpm range.

Checking things at idle isn't the best speed to be looking at.

Fully charged will be 110 - 120 on both sides with compressor off.

 

Before you do that, check the pins and connection to the compressor. We chased a "fault" and come to find out the pins were corroded. We cleaned them off and used dielectric paste (I think) And it now runs like a champ. Hope this helps.

 

thermo what?

 

I had a '05 9900 and I would always have to play with the compressor relay to get it working. One of the "sockets" that the relay pins plugged in to was bad. Fixing it right would have forced me to take the whole panel out. I found out that just plugging the relay in about halfway would make it work... sounds weird but it worked...