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Hi guys. I have a 2017 Chevy sonic at the shop. Long story short the ac compressor isnt being commanded on by the control module. if you go in on the scan tool you can turn it on and off and it works. Confirmed with test light at relay, the ecm will command the ground to the relay if you command it with the scan tool, now when you turn the ac on at the control module, the light comes on and it does not activate the relay with a ground. i found that this command should be controlled by the low speed gmlan, so i unhooked the battery and checked for continuity between the hvac control module and the obd2 connector and found that it does have continuity. ac pressures are checking out on the pressure sensors and on the manual gauges. the vehicle was in a front end wreck and the ambient air temperature sensor circuitry is destroyed, im curious if this sensor may have so kind of control over the ac compressor kicking on, i followed the ambient air temp sensor wiring and it shows on the diagram it is powered and returns to instrument cluster module. which also ties into the low speed gmlan. also weve replaced the control unit once already and i know new parts can be defective but i just dont know exactly how i would go about confidently diagnosing that its bad, being that i dont know much about reading the waveforms on Bus/can/lan stuff that well. any help would be appreciated!!!
Hi guys. I have a 2017 Chevy sonic at the shop. Long story short the ac compressor isnt being commanded on by the control module. if you go in on the scan tool you can turn it on and off and it works. Confirmed with test light at relay, the ecm will command the ground to the relay if you command it with the scan tool, now when you turn the ac on at the control module, the light comes on and it does not activate the relay with a ground. i found that this command should be controlled by the low speed gmlan, so i unhooked the battery and checked for continuity between the hvac control module and the obd2 connector and found that it does have continuity. ac pressures are checking out on the pressure sensors and on the manual gauges. the vehicle was in a front end wreck and the ambient air temperature sensor circuitry is destroyed, im curious if this sensor may have so kind of control over the ac compressor kicking on, i followed the ambient air temp sensor wiring and it shows on the diagram it is powered and returns to instrument cluster module. which also ties into the low speed gmlan. also weve replaced the control unit once already and i know new parts can be defective but i just dont know exactly how i would go about confidently diagnosing that its bad, being that i dont know much about reading the waveforms on Bus/can/lan stuff that well. any help would be appreciated!!!
Yes please the ambient temperature sensor has a role it play with the way the a/c works, so
Please if you
Could find one and fix that will be good. Don’t understand estimate sensors , get the ambient sensor and fix please
Christ De Way Maker
Last edit: 1 year 10 months ago by Chad. Reason: Changed quote color from black to white.
The Ambient Air Temperature sensor can definitely be a player in allowing compressor operation.
First thing I'd suggest is checking the A/C Permission and HVAC Sensor Data lists in the HVAC module. These will give you a decent idea about if the HVAC module is allowing compressor engagement or not. If it isn't, look at the HVAC module inputs. If it is, look towards the PCM.
These values were taken from at 2016 Cruze, A/C working normally:
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