1996 Chev Lumina [car,not van] question

[daveshoe]

My daughter's Lumina temp control for the heater is ''stuck'' on hot. The air temp out the HVAC vents does not change with changes in the temp control. All the otrher heater controls work[fan speed,and control that determines which vent the heat exits from] I pulled every fusefrom the interior panel and they checked out OK. The temp control appeards to be a rheostat,but I do not know what else to try to diagnose the problem. I also tryed to turn the AC on,but the compressor would not cycle. This could be related to the outside weather being below freezing,as my other car would not cycle trhe compressor either

Any help or suggestions would be appreciated.

 

[AKAMAC]

Check the valve that feeds the heater. Follow the heater hoses to the fire wall. The valve should be located next to the firewall in-line on the supply hose. Probably loss of vacuum, they fail open.