Sometimes I have to cycle the ignition to get the AC to kick on
06-02-2014, 07:26 PM
#2
not sure what/why/how you are asking.
can you be more specific? such as are you asking to get the AC compressor to kick on?
and are you saying you start the engine and turn the hvac module to AC and the compressor doesn't kick on, but then you turn engine off and restart and then it does?
if that is the case, it doesn't make sense. i can tell you when you call for AC (for the AC compressor to kick on) the HVAC module sends a signal to the PCM requesting the AC compressor to run. If certain conditions are met then the PCM sends power to the AC compressor clutch which then makes the AC compressor run. there are quite a few things in the chain of events that can prevent the ac compressor from turning on, so it would be helpful to know under what other conditions your problem is happening. and yes if the AC system is low on refigerant then the AC pressure switch would trip and tell the PCM there's not enough system pressure before it's started and the PCM would not command the AC compressor clutch, and i think there might be a DTC trouble code set i'd have to look through the service manual.
but some other things i know from the service manual (if it's correct) "the AC compressor clutch is turned off due to cold ambient air temperatures, the compressor will not come back on until ambient air temperatures reach 5°C or 41°F." so, if you've hacked your pcm or done some stupid mods... like fake out our IAT sensor to read a low temperature in the hopes of always having maximum ignition timing for power, you might prevent your AC from ever coming on.
just found it- the pcm will engage AC compressor clutch any time it's requested and engine speed is below 5000 rpm unless any of the following exist:
- throttle angle is 100%
- vehicle launch
- idle quality
- ac pressure sensor above 410 psi or less than 30 psi
- engine speed more than 5500 rpm
- engine coolant temp greater than 250°F for v-6 and greater than 257° for LS1.
- transmission shift
- torque load
- top of travel clutch switch position if equipped
can you be more specific? such as are you asking to get the AC compressor to kick on?
and are you saying you start the engine and turn the hvac module to AC and the compressor doesn't kick on, but then you turn engine off and restart and then it does?
if that is the case, it doesn't make sense. i can tell you when you call for AC (for the AC compressor to kick on) the HVAC module sends a signal to the PCM requesting the AC compressor to run. If certain conditions are met then the PCM sends power to the AC compressor clutch which then makes the AC compressor run. there are quite a few things in the chain of events that can prevent the ac compressor from turning on, so it would be helpful to know under what other conditions your problem is happening. and yes if the AC system is low on refigerant then the AC pressure switch would trip and tell the PCM there's not enough system pressure before it's started and the PCM would not command the AC compressor clutch, and i think there might be a DTC trouble code set i'd have to look through the service manual.
but some other things i know from the service manual (if it's correct) "the AC compressor clutch is turned off due to cold ambient air temperatures, the compressor will not come back on until ambient air temperatures reach 5°C or 41°F." so, if you've hacked your pcm or done some stupid mods... like fake out our IAT sensor to read a low temperature in the hopes of always having maximum ignition timing for power, you might prevent your AC from ever coming on.
just found it- the pcm will engage AC compressor clutch any time it's requested and engine speed is below 5000 rpm unless any of the following exist:
- throttle angle is 100%
- vehicle launch
- idle quality
- ac pressure sensor above 410 psi or less than 30 psi
- engine speed more than 5500 rpm
- engine coolant temp greater than 250°F for v-6 and greater than 257° for LS1.
- transmission shift
- torque load
- top of travel clutch switch position if equipped
06-08-2014, 08:10 AM
#4
based on that, i would get a tech2 scanner or something similar that will show you real time PCM data to see what's going on and monitor the AC clutch turn on parameter (or whatever it's called in GM speak). my guess is since it does work, you might have a faulty electrical connection somewhere causing the AC compressor to randomly work. whether the PCM commands the ac clutch on depends on those parameters i listed, so you would want to monitor those for starters. good luck.