Chrysler Repair: 02 T&C: A/C problem; BCM or ECM the cause?, 4 digit numbers, volt ohm meter

Question
QUESTION: I have had my mini van servied for ac issues, the auto mechanic has told us that, it needs a new "Main Computer" which would need to be programmed at the dealer???  All components of the AC unit are charged and function properly if he jumpers across a relay,
I have researched and see that this van has two control modules, one and ECM the other a BCM...I am considering getting a new BCM as I think tghis is what ultimately controls the AC unit...All other electrics in the van function properly...Can you please advise???

ANSWER: Hi Alf,
Use you ignition key to see what fault codes are stored in all the modules: 'on-off-on-off-on and leave on" doing that in 5 seconds or less elapsed time. Then watch the odometer window to see the mileage reading change to show 4-digit numbers preceded by a P. Let me know what those are and we'll see if they explain your problem. There are other possibilities we can discuss later too.
Roland

---------- FOLLOW-UP ----------

QUESTION: there are 4 codes on this,,,,
1684
0645
1598
1599

please advise

Answer
Hi Alf,
None of those codes suggest a problem with the bcm or pcm. The 1684 simply means that the battery was disconnected from the system recently.
The 645 says there is either a short circuit or open circuit in the ac clutch relay control circuit, which would a reasonable cause of your problem. I would be pleased to send you an email copy of that part of the circuit from an '04 manual on CD (if it is identical to the '02 which I have a hard copy of and could photocopy and postal mail to you if necessary). Then you can trace the circuit and find the problem with a volt-ohm meter.
The 1598 and 1599 say that the refrigerant pressure in the system were alternatively too low and too high sometime in the recent past which maybe was detected when the shop was filling the system. If you disconnect the battery for a few moments and the reconnect, it erases all the codes except the 1684 of course, and then you can see if either of the last two codes still apply, But the first task is to correct the compressor clutch circuit. You might try a different electrical shop if you don' want to troubleshoot this yourself. But no need to buy a pcm or bcm for sure.
Roland
PS If you want the relevant circuit page send me a follow-up question but use the 'private' option and tell me you email account or you postal mailing address.