Stuck heater control valve?

[tkelley72]

Just went out and started my 72 with AC just to make sure it would start. I had a previous problem with the needle and seat and got guidance here from several of you guys. My question is this: I noticed that both the supply and return hoses going to the heater were "hot". I checked the controls position inside and the controls are set to vent and nowhere near the heater position. Does this mean that the heater control valve is stuck open? Makes sense, right? Can't really check air temp from the supply registers since the temperature here in Dallas has been 107 for the last month. Thanks for your input!

 

[Kilgon]

Problem could be in several areas. I would have someone watch the heater vacuum valve and see if it moves when you turn the heater on and off. If it is opening and closing, then you should be ok unless the actual insides are corroded away. If it is not opening, then you need to check for vacuum. Could be a leak in the hose or possibly the selector itself could be the issue.

Attach is the vacuum routing and a how to test to see if everything is working ok. Good luck.

 

[Hemikiller]

The heater valve is controlled by the vacuum switch on the heater box itself. The blend door arm pushes in the plunger when the selector is placed in the Cool position. It's not uncommon for the cable to slide in the clamp on the box.

 

[73inNH]

In case it helps . . . my heater valve was stuck on cold. When I took it off it was gummed up with crud.

Let it sit for a few hours in vinegar, flushed the cooling system and I had a working heater control valve.

 

[70cobrascj]

I would like to understand this system better.
My questions are: Do only A/C cars have this heater control valve?
Does it keep hot coolant from flowing to the heater core when not needed?
Can this valve be removed?

 

[tkelley72]

Problem could be in several areas. I would have someone watch the heater vacuum valve and see if it moves when you turn the heater on and off. If it is opening and closing, then you should be ok unless the actual insides are corroded away. If it is not opening, then you need to check for vacuum. Could be a leak in the hose or possibly the selector itself could be the issue.

Attach is the vacuum routing and a how to test to see if everything is working ok. Good luck.

Based on the input from Kilgon and Hemikiller, I at the least need to adjust the control cable based on the selector movement. I'll have to check the operation after making those adjustments. Can you tell me the normal position of the control valve movement arm when the engine is off? Currently mine is in the fully extended position. Is this open or closed? I can manually move the arm to the fully retracted position with my hand so it doesn't appear that it is stuck internally. Thanks again

 

[Hemikiller]

I would like to understand this system better.
My questions are: Do only A/C cars have this heater control valve?
Does it keep hot coolant from flowing to the heater core when not needed?
Can this valve be removed?

- Only AC cars have the valve
- Yes, it stops the flow of hot water through the heater core
- If the valve isn't present or functioning, your AC will never get cold.

Based on the input from Kilgon and Hemikiller, I at the least need to adjust the control cable based on the selector movement. I'll have to check the operation after making those adjustments. Can you tell me the normal position of the control valve movement arm when the engine is off? Currently mine is in the fully extended position. Is this open or closed? I can manually move the arm to the fully retracted position with my hand so it doesn't appear that it is stuck internally. Thanks again

The valve is normally open. You can hook it up to a manifold vacuum source to test it.

 

[70cobrascj]

So not flowing water thru the heater core doesn’t cause any problems with the Cleveland or the 429?
If so I assume you could just plug the heater core hose fittings off?