passenger temp control module....or is it?

[trouttrooper]

Before I just go replacing parts I wanted to ask you guys first. My 03 Envoy XL SLE has manual temp controllers and the last few days the passenger side has been acting up. It will blow hot air with the temp controller set at hot, but occasionally all on it's own the temp will suddenly go to full cold. It will stay cold until I move the temp controller to full cold then back to full hot. Then it will blow hot air again. Is this the control module going bad or something in the sliding control switch going bad or something else?

Thanks.

 

[The_Roadie]

Could be anything in the control loop. Actuator, actuator position feedback sensor wiring from the actuator back to the control module, or the control module. Could be diagnosed only by being able to monitor the voltages on all five wires at the controlled and see what they read when it works and when it doesn't work.

As a first step, I'd unplug and replug the connectors at the control module and at the actuator in case a contact is oxidized and went flaky. Inspect the harness for chafing and worn insulation that might be shorting out to sharp sheep metal edges of dash support brackets.