heater/ac problems

[billnorthincolo]

My 95 S-10 Chevy and my 2001 GMC Jimmy both have this problem. Sometimes, usually in the summer, the heater blows full hot no mater what the temp control is set at. Then again, sometimes the a/c blows full cold, usually in the winter time, no mater what the temp control is set at. Any ideas? Thanks

[Blue Bowtie]

Both of those still employ the vacuum switch on the HVAC controls to operate the air doors and diverters. If the air is discharged from the correct outlets at the various settings, such as defrost, floor, and vent the vacuum servo system is working properly.

Both of those also employ the differential resistance type actuator for the temperature blend door. The control in the instrument panel is merely a resistor that drives an electric actuator, and the feedback potentiometer (slidewire) within the actuator balances the resistance of the control knob.

If the only problem is temperature regulation there may be problems with the potentiometer at the control knob, the feedback potentiometer in the actuator, the actuator driver (within the actuator) or the wiring. Simply cleaning the potentiometer on the IP control can resolve these issues sometimes. Use a cleaner designed for the purpose and one that is safe for plastics, such as Caig DeoxIT or CRC QD cleaner. Follow the instructions and be certain to exercise the control upon cleaning to wipe any contaminants and oxidation out of the potentiometer contacts. The same may have to be done with the blend door actuator.

If cleaning does not restore performance, further diagnosis may be necessary.

[j cAT]

Originally Posted by billnorthincolo

My 95 S-10 Chevy and my 2001 GMC Jimmy both have this problem. Sometimes, usually in the summer, the heater blows full hot no mater what the temp control is set at. Then again, sometimes the a/c blows full cold, usually in the winter time, no mater what the temp control is set at. Any ideas? Thanks

the 95 s10 has a vacuum controlled ac system. I would locate the vac ball and check the vac line also using a vac gauge see if the ball holds vac with the engine off. there is a check valve to make this vac stay in the ac system . most times the vac line is damaged at the TBI. could also be dirt causing the temp door to stick. 2001 s10 don't know..