Heater box under dash still hot when switch and valve are off
My 1964 factory air car's heater/air "box" under the glove compartment gets hot when running for even short cruises. The longer...the hotter. I have checked the cable pull on the dash to make sure it is opening and closing the switch on the heater box (behind glove comprtment on top of heater/air "box")...have replaced that switch itself (as a precaution) that controls the vacumn valve that lets water in the heater core...and have replaced the vacumn valve in the engine compartment... yet still the heater box still seems to partially fills with hot water and heats up the heater /air"box" under the dash over time and makes for a hot floor board after a few miles. Also I have checked the exhaust to make sure the heat shields are in place and nothing is touching or too close to body...all appears OK. Is there something I am missing that keeps the water out of the heater box when the cable pull switch is off on the dash and the valve is working? Does natural pressure in the engines water system cause a back up in the heater core that can't be avoided? Thanks for all replys.
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Re: Heater box under dash still hot when switch and valve are off
John,
By factory air - you mean that its the AC system installed at St Louis?
If yes, then there is something wrong.
If water is getting past the valve that shuts off water flow, then that is the first place to look, valve may be new, but that does not mean it works. Did you look at it that it actually has the flipper or door inside? Can you see it move when you activate the system? -
Re: Heater box under dash still hot when switch and valve are off
You could try a separate direct hook up of full time vacuum to the water vacuum valve and see if this makes a difference. Also you could use a vacuum pulling tool to test the vacuum water valve to see how long the valve would hold the applied vacuum.Comment
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Re: Heater box under dash still hot when switch and valve are off
For the 1963-67 factory AC cars (and possibly some of the early C3), the hot water valve to the heater box is supposed to be CLOSED with no vacuum and OPEN when vacuum is applied. In the later cars this was reversed. So to stay cool, you want to ensure that this valve does not have vacuum applied to it. You can simply disconnect and plug the vacuum hose.
I would check the heater hoses with the car operating to see if this valve is fully closed, or appears to be leaking through. An IR thermometer may help. You can also pull this valve and check it on the bench....then reinstall it.
Some folks also add a manual shutoff valve in the heater supply hose closer to the intake manifold, where access is better.
Remember that the outlet hose from the heater does not have a valve, and that the hot water temperature will migrate or conduct back through the outlet hose to the heater. So this hose will be warm/hot. However, unless the hot water valve is leaking through on the supply, this migration/conduction should not provide a lot of heat input into the heater box.
Make sure you have the correct hot water valve for the C2 cars (closed with no vacuum... and requires vacuum to open). Also check the the valve to make sure that it does not have vacuum when the dash knob is set to COLD. This could be due to a faulty switch or switch positioning on the heater box. I have heard of some issues with the reproduction/replacement heater box cable-vacuum switches.
LarryComment
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Re: Heater box under dash still hot when switch and valve are off
Since the water control valve is closed with no vacuum applied, you might disconnect/plug the vacuum line at the valve & see if it helps.
If yes, then that suggests that the brass vacuum switch is the culprit.
If no change, then the water control valve is probably defective.
You ask a good question though as to whether the valve, by design, should be able to remain closed with 15psi of coolant pressure bearing on it. Hopefully yes!Comment
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Re: Heater box under dash still hot when switch and valve are off
Thanks to all...some great info...will check out and advise!
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Re: Heater box under dash still hot when switch and valve are off
John some good posts concerning this from June 22, 2005 at the bottom of this posting.Comment
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