PLEASE DON"T BLAST ME FOR ASKING THIS QUESTION, I DID LOOK!

Back in mid December I acquired a nice example of a '00 S-type 4.0, silver, black interior. Motor rebuilt at 97k and several TSBs completed. I have been steadily adding stuff and fixing stuff here and there. New black headliner, black/grey seat covers (f&r), 19" XJR wheels, Thrush dual in/out muffler and straight pipes out the back, CAI and tuneup.

Well one of the last things I need to do is fix the A/C. It wouldn't get cold. I mean nothing. I began checking the normal stuff, charged the system, checked the pressure switches, relays and fuses, but no power to compressor or cooling fan when A/C is selected. The CCM seemed to be functioning. I jumpered out the compressor clutch and it works fine, no cement mixer noises either, but no cold air. Being a full time student, I didn't have the time to dig into the A/C troubleshooting any further, so I took it to a well respected shop here in the area and they have narrowed it down to this:

Power source to fuses and relays- GTG (Good to go!)

A/C Control Module performs all of its functions as far as they can tell; i.e. Turns on/off, Auto select, temp select works both left/right, flapper doors, etc......

They read out everything, pressure switches, compressor, DCCV, all the way to the PCM/ECM They found the blue and brown wire to pin 9 and ground them out. Everything started working. A/C got cold, cooling fan turned on, etc....

So do I need a new PCM or a reprogram?
Maybe a new A/C Control Module? They doubt it, but it is a Jag.
Can I add a switch to ground out the two wires and just go?

Summer is here and adding the black headliner, even though it looks sweet, it is going to be hot.

 

Did they check the cabin temperature sensors (drivers and passenger side dash)?

 

They didn't mention that, so maybe not. I know I cleaned the one next to the ignition switch.

 

I believe Jag diags can read each of the multiple temp sensors to see if they're OK. Don't forget the exterior one - at about $10-15 you may prefer to just change it. (That's for the 03+ cars, don't know about yours. Just behind where the front license plate is / would be. 5 mins to change.)

 

When the system was temporarily run, did cold air blow from all the vents and heat from others? if yes, then CCM.

 

No cold air period. Compressor wouldn't come on at all until I jumped it, but no cold air. The guys at the shop ground out the Pin 9 wires and everything worked as it should. Compressor and fan turned on, air got cold.

By the way, it does get hotter as higher temp is selected, so that part works and the I guess the DCCV is working correctly too.

 

Gross, Just re read your post. Its too early and not enough coffee yet. Anyway, when the shop ran the A/C temporarily it got cold and they didn't mention any vents blowing hot.

 

Just because your compressor runs does not mean it is fully functional. During the past couple of years, several of us have had to replace our compressors. Ours indeed sounded like a cement mixer when I listened to it through my mechanic's stethoscope, but other owners here reported that their compressor did not sound unusual when it failed. I suspect your compressor is indeed the culprit here....

 

The jag diags (and AE - AutoEnginuity) can also read the HiLo pressure switch. If it's faulty it can in effect be telling the PCM not to run the a/c.

 

The press switches and compressor read out good when they put it on the Diagnostic Machine. So, I am going with a switch to ground out the wires at pin 9 to turn the A/C on and off.