GMC SIERRA AC Problem

RWEITKNECHT · April 27, 2017

My truck is a 2011 GMC Sierra 1500 V8 5.3 L 4WD.

My A/C does not work. The system has been evacuated and recharged to specifications. The low pressure switch and electrical connector has been replaced. The last time I checked the pressures it was 70 deg ambient and had 40 psi on the low side and around 150 psi on the high side. The last place I took it to told me that it was the HVAC control module. I replaced that and it didn't solve the issue. I can get the A/C to turn on and blow cold air by jumping between 87 & 30 on the AC Clutch Compressor relay. That relay feeds a 10A amp fuse which goes to the clutch switch. I have checked the relay and it is fine. I am wondering if either the ECM is locked up or if a temp sensor somewhere is telling the compressor not to come on. Any further advice on this would be greatly appreciated.

GMCustomerService · April 28, 2017

Good Afternoon Robyn,

We regret to hear of the concerns that you have been experiencing in regards to your Sierra and we certainly recognize your frustration. Please know that we strive to provide you with a reliable product, and do further apologize if you feel this has not been the case. Our team would be more than happy to reach out to your dealership to further discuss this A/C concern. To do so, please send us a private message that includes your VIN, current mileage, full contact information, and the name of your preferred dealer. Thank you and we look forward to hearing from you.

To learn more about GM's privacy policy, please visit https://www.gm.com/privacy-statement.html.

Best,

Philip J.

GM Customer Care

silveradosid · April 30, 2017

is this auto temp control or manual

RWEITKNECHT · May 3, 2017

It's automatic but you have the option for manual operation. So I took it to the dealer and they are telling me it's the evaporator temperature sensor and it's going to cost me about $900 bevause you have to remove the entire dash and evaporator box to get to it. A lot of money for a $30 part. They also said my dash is cracked and would have to replace that as well which would be another $500.

I decided to try to bypass the sensor using a resistor with the proper resistance that the computer would want to see to engage the compressor. I took some resistance measurements of the new sensor to make sure I was in the same range. I still cannot get the compressor to come on. I am getting 2.5 volts out to the sensors from the control module and I'm hoping that is nornal.

If anyone has had any success with bypassing one of these sensors I would like to hear how it was done.

silveradosid · May 3, 2017

That sensor is just an on off switch there should be zero ohms or nothing

RWEITKNECHT · May 3, 2017

The evaporator temperature sensor on my truck is a thermistor which is essentially a resistor that has varying resistance with temperature. So when it gets hot it should tell the compressor to kick on. I basically used a resistor that has resistance that corresponds to the ambient temperature. I am starting to wonder if this is actually my problem.