I have vacuum to the control valve until I move the lever to put the heat on in the car, then there is no vacuum to the control valve. Checked the vacuum lines and all seem to be in good condition. Coolant is full. Any more things I can check? I also can tell you that the inlet and outlet hoses are hot. The control valve was also replaced. Thanks for you help Denny

 

Have you checked the control head and its hoses to make sure that vacuum is getting there? It sounds like maybe something is hooked incorrectly.

 

I am not sure what the control head is, but I can tell you that I have had this car for about six years now, and the heater was working fine. Then one day it did not work. I replaced the control valve. Checked the hoses and vacuum lines. There is hot hoses going in and coming out .I looked at all the vacuum line connections going to and from the heater and they all look ok to me. Something has to be failing. What about the other two switches that vacuum is connected to. I believe one is an actuator valve,and a switch vacuum water valve control. Do you have any idea on how to check if these are good or bad?


Thanks for your help

Denny

 

I think you may be looking in the wrong area. Your description tells me that hot water is flowing through the heater core. That is controlled by the valve in the engine compartment that you replaced. Now you need to check the diverter doors in the heater box, if I remember correctly, three doors direct the air-flo and are controlled by vacuum and /or cable from the heater control on the console.

 

OK - Let's see if I understand this correctly. You have had the car 6 years and all has been well. You have replaced the heater control valve and you have a vacuum signal present at the control valve - so that is good.
Now we need to see if coolant is getting to the heater core and passing through it or not. The heater core is like a little radiator - hot coolant passes through it and air passes over it and gets warmed up. After the air gets warmed up it gets directed to the air vents and either the windshield, the center vents or the floor. This is what 73 and 78 are talking about, the vent doors that control the direction of the air flow.
Getting back to the heater core - usually when they fail they leak, but it is also possible that it has gotten full of crud internally and is not allowing coolant to pass through it. There is also the chance that a heater hose is kinked or pinched shut, but you have had the car 6 years so this is less likely. It is also possible that a heater hose is full of crud and blocked. After 30 years of service, six of them with you, have you ever flushed your 'Vettes cooling system?

My .02

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Thanks I will look into these suggestions and let you know how I make out.

Denny

 

Does this help? http://www.home.comcast.net/~chadwic...entilation.htm PG.

 

Interesting site. Was hoping he'd say something about putting in a C4 fan and motor. Saw something about that one time. Supposed to move a lot more air.

 

Hi 73shark, look on the left side under "Table Of Contents" "Upgrading The Fan", is that what your looking for? PG.

 

can any one tell me is it possible to look into the heat box of a 1978 to see if a mouse has built a nest and keeping the doors open or closed? Or do I have to take it apart.