Hi Everyone. I am having a similiar issue on a 2007 Acadia. My compressor is cycling with permission withheld and permission granted erractically like the system was low on gas. I can command on in the ecm module and runs fine. Plenty of gas and good pressure. All sensors read normal. Pressure sensor, Ambient Sensor, Coolant Sensor etc. I can pull the A/C relay and still have the erratic permissions on and off. I can bypass the relay and compressor works fine also. Also when this started I also see the instrument guages making erratic movements. when i command the compressor relay on through the ecm it all stops. Question what would cause the erractic guages and a erratic signals to the compressor relay. Check the wiring harness completly in the engine bay. Ironically I had a 2007 acadia that everytime I turned right the whole instrument cluster went dead. that turned out to be a chaffing wire by the tail gate.
NEED HELP 2007 Acadia A/C Permission Withheld
- Thread starter rickknapp
- Start date
Should be in its own thread, as the Acadia is a completely different animal..
That being said, you said it has plenty gas... How do you know that?
You didnt mention pressures, so it could be working on low pressure, which will cycle the compressor, until the PCM says no more, and disables it, or it could even keep cycling it, until the clutch blows a horrid death.
What are the pressures, low and high?
That being said, you said it has plenty gas... How do you know that?
You didnt mention pressures, so it could be working on low pressure, which will cycle the compressor, until the PCM says no more, and disables it, or it could even keep cycling it, until the clutch blows a horrid death.
What are the pressures, low and high?
Erratic gauges suggests a wiring problem in the Class 2 Serial CANbus. Ditto if bypassing the A/C compressor relay works. What kind of scanner did you use? Is it able to detect BCM (Bxxxx) or network (Uxxxx) codes? You might want to check the connectors on the BCM & the splice packs by giving them a good wiggle while the A/C is off and then checking the gauges for any erratic behavior.
Edit: Should read CANbus and not Class 2 Serial
Edit: Should read CANbus and not Class 2 Serial
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low side psi 45 high side 240. Does the same erractic behavior of withdrawing and granting permission to the ac relay when the relay is removed and compressor not running. I have an autel maxicom 908p. can read all modules and codes. No B our U codes detected.
Sounds like noise on the bus data lines. The link below has a good summary on diagnosing CANbus issues.
Diagnosis on CAN-bus
There are some additional articles on this site about using oscilloscopes to debug data bus problems.
Diagnosis on CAN-bus
There are some additional articles on this site about using oscilloscopes to debug data bus problems.
Mooseman
Moderator
If you can, look up what the HVAC module is doing if your scanner can show live data. Maybe it's the one that's sending bad commands. Another thought is that the external temp sensor is bad making it think it's below freezing intermittently. I don't know if it's the HVAC module or the PCM that stops compressor function below freezing so check both.
It cycles on and off about 10 to 15 times per 60 seconds. It has to be an erractic signal in the logic tree before being sent out of the ecm to the a/c relay. Like I said when i command the a/c relay, compressor runs non stop and pressures are good. Air is cold.
All live data is fine. Nothing is showing any erractic movements like permissions and a/c relay on and off.
Mooseman
Moderator
Also replaced alternator thought maybe a power surge was happening from the voltage regulator. That made no difference.
Mooseman
Moderator