Trying to get A/C request with PCM Serv. No. 12576106 (2003 Express)
07-11-2011, 08:53 AM
#1
Trying to get A/C request with PCM Serv. No. 12576106 (2003 Express) This PCM is supposed to be out of an 2003 Express van. I tried wiring up the A/C +12v request to pin 17 (green) which should drop ground to pin 43 (green) when +12 is applied to 17. Nope, doesn't do anything when I put 12v to 17. I am running a huge cam and will need the PCM to see the a/c request.
Any tips? On the Express van there is no A/C pressure input, the wiring schematic shows +12v coming from the a/c controls, that goes through a high pressure switch then to the pcm pin 17, then the pcm drops ground to pin 43 which goes to the clutch relay then on to a low pressure switch and then to the compressor.
Soo, if I apply +12v to pin 17 why would I not be getting ground at pin 43?
Anything I can do in HP Tuners?
Any tips? On the Express van there is no A/C pressure input, the wiring schematic shows +12v coming from the a/c controls, that goes through a high pressure switch then to the pcm pin 17, then the pcm drops ground to pin 43 which goes to the clutch relay then on to a low pressure switch and then to the compressor.
Soo, if I apply +12v to pin 17 why would I not be getting ground at pin 43?
Anything I can do in HP Tuners?
12-01-2015, 11:06 PM
#7
PCM must see both inputs before compressor operation is allowed
AC request 12v passes through normally closed high pressure switch to the pcm
Ground goes through the normally open compressor clutch low pressure switch but low pressure switch is closed with refrigerant in system and opens during compressor low pressure condition such as cold coil during low blower air flow.
PCM sees 12 v on request and ground from the LPS this verifies both safeties are operational and pcm allows compressor operation and then grounds the compressor clutch relay coil to turn on the compressor. The LPS switch then cycles the compressor as normal when needed during operation to prevent coil freeze up and liquid slugging that will blow valves in the compressor.
AC request 12v passes through normally closed high pressure switch to the pcm
Ground goes through the normally open compressor clutch low pressure switch but low pressure switch is closed with refrigerant in system and opens during compressor low pressure condition such as cold coil during low blower air flow.
PCM sees 12 v on request and ground from the LPS this verifies both safeties are operational and pcm allows compressor operation and then grounds the compressor clutch relay coil to turn on the compressor. The LPS switch then cycles the compressor as normal when needed during operation to prevent coil freeze up and liquid slugging that will blow valves in the compressor.
