Correct Operation Of Heater Control Valve

[ndccpf1]

Have a 98" B4000 (5 spd) and recently took notice on the Heater Control Valve and when it should "operate / move". I have done the blend door fix and I have also replaced the Heater Control Valve some years back.

When truck is "OFF" and I pull the vacuum line off the HCV, the pivot arm will move "down" and I can put the vacuum line back on the HCV and the pivot arm pulls back "UP".

While truck is running, and I move the heater panel knobs (temp / position) I do not see movement of the HCV. Will it move at certain engine temp ? I do know moving the temp knob will move the blend door motor / door.

Thanks in advance.

 

[92 5 oh]

It's been a while since i messed with mine, but i seem to recall that the bypass is open when there is vacuum present, in other words coolant goes to the heater core when vacuum is at the actuator. When there is no vaccum the bypass closes and coolant does not go to the heater core. when the AC is in "normal" I believe there is vacuum at the bypass but when the AC is in max there is no vacuum. so, if i remember correctly, the bypass is closed (no vacuum) and coolant does not go to the heater core only when the vehicle is off or the AC is on Max. Check and see if that's the results you get and post back.

 

[ndccpf1]

You are correct I did the full range tests this morning. ONLY when MAX A/C position is chosen will there be no vacuum and hence movement of the piston "down" in the direction of the engine

Thought I had ran the knob cycle but I had an assistant the last time who was going on my directions (they did not listen )

Enjoy the weekend !

 

[sebastian323]

Is there a manual control valve that I can install to replace the vacuum valve ?

 

[RonD]

Is there a manual control valve that I can install to replace the vacuum valve ?

This thread is from 2014

Google: 4-way Automobile Heating Water Valve, Brass Automotive Integrated Manual Control Valve

But you can just control your current one manually
Its vacuum operated and its in the engine bay so........................................
Just hook it up to engine vacuum and it by-passes heater core, full time
Unhook it and plug the engine vacuum hose and its not by-passed

 

[sebastian323]

This thread is from 2014

Google: 4-way Automobile Heating Water Valve, Brass Automotive Integrated Manual Control Valve

But you can just control your current one manually
Its vacuum operated and its in the engine bay so........................................
Just hook it up to engine vacuum and it by-passes heater core, full time
Unhook it and plug the engine vacuum hose and its not by-passed

Cool. If the heater core is being bypassed, can i get cool air (without AC) to the cabin even when my blend door is not working ?

 

[RonD]

Well it would be outside air temp, but yes, heater core wouldn't be heated