heater control switch
 

hey guys,
When i select the upper vents on my 96 Blazer nothing comes out. The defrost and the floor vents work great,also the truck doesnt get hotter than 15o degrees.Are the vents vacuum actuated, if so how would i find the problem
thanks


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RE: heater control switch
 

When you change modes on the HVAC controls, do you hear things changing in the dash or does air only come out of the defrost and floor vents regardless of HVAC control position?

Yes, most of the actuators for the HVAC system are vacuum actuated. A vacuum problem in the supply line would force the system to its default position which is defrost + floor.

RE: heater control switch
 

yeah its only floor and defrost no matter were hvac is,its not making any noise in the dash at all.are the supply lines up in the dash or under the hood?

RE: heater control switch
 

Vacuum supply comes from the engine.

RE: heater control switch
 

Several good posts on this subject...https://blazerforum.com/m_110485/tm.htm, that said...I flushed my 99, radiator, block, and heater core today, replaced the thermostat w/ 195 deg new and coolant, and went from 80deg output to 160deg! Truck had recently started running cool, I suspected weak / wide open thermostat. Now reading 197deg at thermostat housing, 150deg radiator inlet, 95deg outlet(60 deg outside today), Temp gauge reading about 200deg.
My selector switch had also quit working, verify that the vacuum line located near ABS unit... near the driver fender is attached...you can test by blocking it off...mine had come loose and was just enough of a leak to affect my selector switch, all is now good again!