No Heat--Water Valve?

BASS

Member
Joined
May 25, 2001
Ok, when I put the slider to Hot on my car, cold air blows out. I checked the water valve (which I had replaced with a new GM one a few years ago), and the plunger definitely works when the slider is moved from Hot to Cold and vise versa. I checked the hose from the valve to the heater core along the firewall, and the hose gets hot, so it looks like the valve definitely works. Also, I can hear the shudder door move when the slider is moved, so I dont think theres a problem with the door or the blower motor..

Any idea what it can be? Could it be that the water valve went bad again? Heater core? :mad: Low coolant? :confused:
 
Is the linkage moving when you turn on the heater? Have someone actuate the lever while you watch it. If that isn't possible take the valve out and use a hand vacuum pump and you will be able to see the ball valve and tell if it is opening or not. Also double check your hoses and see if any that are not plumbed correctly.
 
There's a vacuum source that connects to the valve that pulls vacuum when you operate the AC/heater controls, plus there's a mechanical slider for hot/cold. Have you verified vacuum on that hose?
 
The plunger on the water valve automatically moves up and down as the slider is moved Hot to Cold, so I know the plunger is working (via vacuum).. Can the water valve still be bad? Also, motor temp goes to the normal 165-170 degrees (verified by scanmaster) and the cooling fan kicks on/cycles normally and upper/lower radiator hoses get warm. If the thermostat is stuck open, wouldnt the scanmaster show much lower temps?

I have a feeling maybe the heater core is somehow bad, but I thought they usually only go bad when they crack/leak coolant (in which mine doesnt)..The car was sitting over the winter and it was normal up until today when I tried it..:confused:
 
The water valve can get mechanically corroded and stick even with vacuum present and not work.

If both heater hoses get hot, inlet and outlet the valve is usually working, but could still be at reduced flow so it's worth checking.

There is the heater slider control that must move the heat door to the proper position so air goes through the heater core and out the vents properly.

It is mechanical via the slider and a cable and not vacuum operated.

It usually can be heard to clunk into position when going from cold to hot along it's travel when operated quickly.

That slider needs to work the door properly for sure.
 
Take your hoses supply and return off and hook up a garden hose to them to see if you can get water to flow through the heater core. If it flows through then I would verify the door opening. If water doesn't flow through then your heater core is clogged. If that is the problem then would have to clean out the core which could be a PITA! In your first post you said the hose at the valve was hot but you didn't say if the other hose for the heater core had any heat. I have never seen a core get clogged but it could happen I guess. Hopefully for you the ball valve isn't opening up all the way. Take the valve off and you should be able to see through it. I think you have to apply a vacuum to get it to open but I may have that backwards.
 
If you open the glovebox & hold the side tab & let it fully hang down (empty it first) then you can watch the temp control slider working. Mine broke years ago but you can usually feel when they do as there is no tension on the slider at all. Altho, this way in 30 secs you know 100% that's it's working properly on the mechanical end.
 
The heater valve is spring loaded to be normally open. When the heater is off, vacuum is sent to the valve to close it. When the heater is turned on vacuum is taken away and the spring opens the valve.

So...... with the car running and the heat off, pull the vacuum line off the valve and see if it opens.
 
The spring gets weak and leads to partial operation, due to corrosion on the rotating valve, a lot more often than the vacuum part of the valve becoming defective.

It's metal, mechanical, and working with water and chemicals all the time.

Checking the door operation through the glovebox is a great idea. :cool:
 
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