miked123

On my 1974 corvette, my heat suddenly stopped working. I was driving to work during a cold day and about halfway there the heat shut off and cold air started blowing(it hasn't worked since). I need help in diagnosing this problem. Any ideas?

Old Ben

Welcome to the forum. The members in the C3 section should be able to help you.

Paul L

Any green fluid on the passenger floor? Apparently your fan is still OK.

Peterbuilt

There is no shut-off valve to stop the flow of water.
Heat is controlled by a flap in the heater core box.
Check that the temperature cable is connected on both ends.

rcread

Is the hose that returns water from the heater core hot when the heat is on?

miked123

no green fluid on the floor.

Paul L

In a 1974 the hose should be hot all the time: there is no control valve. Heat is regulated by a flapper door.

Paul L

Good. The heater core is OK.

DUB

Does you car have A/C???

How hot is your coolant getting when you drive now after this problem started???

DUB

cabman72

Is your coolant level low? Is the engine running hot? If the level is low or the thermostat isn't opening completely, you won't be getting any hot coolant to the heater core and the fan will blow cold air.

Peterbuilt

Or is the thermostat stuck open and the engine is running too cold?

lvmyvt76

low coolant or thermostat is stuck open.

rcread

That's why I asked. If it's not hot, you know hot water isn't circulating through the heater core.

miked123

[QUOTE=Peterbuilt;1593882509]There is no shut-off valve to stop the flow of water.
Heat is controlled by a flap in the heater core box.
Check that the temperature cable is connected on both ends.


Does the temperature cable also direct the airflow? Like wether the air goes to defrost or feet, or face? If so, then mine is ok because when i spin the wheel to heat, the air goes directly to my feet.

miked123

The thermostat is fine and the radiator is full of coolant. I just topped it off a few weeks ago.

miked123

[QUOTE=DUB;1593889461]Does you car have A/C???

How hot is your coolant getting when you drive now after this problem started???


My a/c is broken, the hose connected to the VIR valve is leaking. The cars engine temp varies with outside air temperature. When the outside air is around 50 or 60 degrees, the engine runs around 160-175 degrees.