How do I replace a heater control valve? - 2002 Chevrolet TrailBlazer

This vehicle doesn't' use a heater control valve it has a blend door.

Do you have Manual Climate Control System or Dual Automatic Temperature Control System ?
The temperature control switch:

• is a potentiometer that outputs a variable voltage to the temperature blend door actuator to set the position of the temperature blend door.
• initiates closing of the heater control valve. When set to full COOL, a lever on the temperature blend door pivot shaft depresses the pintle of the heater control valve vacuum switch. The heater control valve vacuum switch then applies vacuum to the heater control valve, closing off engine coolant flow to the heater core.
• is serviced only with the climate control assembly.

You may have disturbed something when changing the actuator , the vacuum switch o vacuum hose .

Either your heater control valve is not properly operating or your heater core is clogged. Locate the heater control valve under the hood, should be close to firewall on heater hose, have someone adjust temperature from hot to cold and see if you can see the heater control valve operating if so replace the heater core, if its not doing anything replace it(heater control valve).

low fluid level or heater control valve may need replace..check hoses going to heater core...if cold...between heater control valve and heater core..replace control valve

your heater control valve should be located on one of your heater hoses coming from the heater core. usually they are located close to the firewall and will have some type of control cable attached to it . Simply unhook the two hose clamps to remove and replace the valve .

there is a vacuum switch inline on the heater hose that is not opening up and letting the hot water go into the heater core.
replace the heater control valve on the heater hose coming from the water pump.

If it's not blowing out hot air, the blend door may be the problem on the 1990 Isuzu Trooper.

Heater Water Control Valve REMOVAL & INSTALLATION On early models the heater control valve was part of the heater core inlet. To replace the control valve, remove the heater core as outlined in this section. Remove the control valve from the heater core, being careful not to damage the core. Use new gaskets when installing new valves. The remainder of the vehicles are not equipped with heater water control valves. They use heater unit doors to regulate the amount of heat entering the vehicle. --- I would check that both tubes running to the heater core are getting hot. If they are, then there is a blend door problem. If both tubes are not getting hot, the heater core is blocked somewhere or the heater control valve, if so equipped, is in need of replacement. Good luck on this repair.

Check the water control valve behind the engine close to the firewall. This valve opens and closes to allow hot coolant to enter the heater core. It is usually connected to the heater controls with a cable. When you adjust the heater control for heat, a cable activated lever on the valve should move and allow coolant to move through the valve. The cable from the heater control can come loose from the lever, or the valve itself can become corroded and hard to move.

The heater bypass valve is bad.It's located on the heater hose under the hood near the firewall.It looks like a little 3in.diameter black disc with a vacuum line attatched to it

the temp blend door may not be rotating from the a/c evaporator to the heater core opening.

Could be the motor on the blend door or the temp control knob.

Do you have manual a/c or electronic temp control?

If it's the a/c door electronic actuator motor, it's on top of the plenum. Have to remove the instrument panel for access.

Hope it's the temp knob on the control head.

top one is the circuit you are looking at