I have a 78 vette and have no heat. I replaced the valve under the hood connected to the heater hose. I can feel heat going in and out of the fire wall. The blower motor just blows cold air. Is there some other switch inside the car to check. Thanks Denny

 

The control valve under the hood is vacuum operated. Sometimes the vacuum lines become clogged and need replacing. Try removing the vacuum line from the control valve and turn the heat control on and off with the engine running - see if you get a vacuum signal at the control valve. If no signal, try checking the connections at the heater control, then replace the under hood vacuum line. Sometimes the under hood vacuum line gets melted from being up against the engine and/or exhaust. I hope that helps!
Another thought - is your cooling system full?

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Welcome to CF, Denny!

DeeVeeEight has got ya on the right track.

 

Hi and welcome to the forum, PG.

 

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

 

Am I responding right here. Since I am new I am not sure I have the hang of how to interact. If I am not doing this right please let me know on the write way to write and respond.

Thanks Denny

 

If ya post in the "C3" forum, you'll get more responces.
Not everyone reads the "New Member" forum. [&o]