Auto Temp Control AC Button Not Working (CJ2, HVAC,15855848)
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CF Beginner
Joined: Feb 2011
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From: Ontario, Canada
Auto Temp Control AC Button Not Working (CJ2, HVAC,15855848)
2005 Chevrolet Suburban Z71 (290K KM) w/RPO CJ2 (HVAC auto temp control)
I've been having issues with my A/C where it will blow warm at idle and cold when moving. To add to this we have experienced loss of refrigerant over the last 2 winters while there are no leaks detected in the system. Also noted through the winter months the heat is not always working at full capacity; it takes a noticeable long time to heat up the interior in similar fashion that it takes a long time to cool the interior in the summer.
As far as the AC goes we've narrowed it down to the AC condenser fan not being turned on by the PCM. My mechanic figures that the refrigerant pressures are getting too high in the winter and the refrigerant is being blown out the pressure relief valve(?). After some head scratching and notation of the winter heat issue the HVAC controller in the dash was tested using a scanner and it was determined that when the AC button is pressed the command to the PCM occurs momentarily and then instantly shuts off. The AC on indicator remains lit on the controller. The electric condenser fan never turns on although when tested it works on command through the scanner.
So the recommendation is to replace the HVAC Controller part number 15855848 which costs about $230 CAD. My hesitation is that I also read that the HVAC controller works with input from several sensors (ambient temp, inside temp, sun sensor, etc...). I've read through multiple posts in multiple forums and I can't seem to find anybody with similar issues. Has anybody encountered this? Does anybody know the locations of the sensors and how to test them to ensure they are working properly? Any other things I should check?
I've read that the inside temp sensor located above the drivers seat for the front HVAC is the same as the rear so I can test that one by switching them out. I know the location of the ambient temp sensor and sun sensor but no idea how to test them. The ambient temperature is likely okay as it appears correct on the rear view mirror display. I'm not sure which other sensors come into play for the front HVAC controller.
I'm hoping that someone will be able to give me some advice before I start throwing parts at the issue.
I've been having issues with my A/C where it will blow warm at idle and cold when moving. To add to this we have experienced loss of refrigerant over the last 2 winters while there are no leaks detected in the system. Also noted through the winter months the heat is not always working at full capacity; it takes a noticeable long time to heat up the interior in similar fashion that it takes a long time to cool the interior in the summer.
As far as the AC goes we've narrowed it down to the AC condenser fan not being turned on by the PCM. My mechanic figures that the refrigerant pressures are getting too high in the winter and the refrigerant is being blown out the pressure relief valve(?). After some head scratching and notation of the winter heat issue the HVAC controller in the dash was tested using a scanner and it was determined that when the AC button is pressed the command to the PCM occurs momentarily and then instantly shuts off. The AC on indicator remains lit on the controller. The electric condenser fan never turns on although when tested it works on command through the scanner.
So the recommendation is to replace the HVAC Controller part number 15855848 which costs about $230 CAD. My hesitation is that I also read that the HVAC controller works with input from several sensors (ambient temp, inside temp, sun sensor, etc...). I've read through multiple posts in multiple forums and I can't seem to find anybody with similar issues. Has anybody encountered this? Does anybody know the locations of the sensors and how to test them to ensure they are working properly? Any other things I should check?
I've read that the inside temp sensor located above the drivers seat for the front HVAC is the same as the rear so I can test that one by switching them out. I know the location of the ambient temp sensor and sun sensor but no idea how to test them. The ambient temperature is likely okay as it appears correct on the rear view mirror display. I'm not sure which other sensors come into play for the front HVAC controller.
I'm hoping that someone will be able to give me some advice before I start throwing parts at the issue.
