Heater blows cold air when car is not moving
 

My heater blows out hot air when i am driving but if I am sitting still at a stoplight or even when the car is stopped while warming it up, only cold air comes out of the vents. it is only when I start moving again that the air heats up again. This happens even when the coolant is 200 degrees, so the engine is not cold.

I have always thought that the air was not very powerful coming out of the vents as well, compared to other cars I have had.

check your water level may be low

This happens to me, as well... and I know my H2O is full.

Low coolant is certainly a suspect with any heat/cool condition, but

There is a "door" that opens and closes at the heater box to close off or allow cold air. The door is controlled, I believe, by the temp controls on your heat/ac switches. The vette circulates coolant continuously through the heater, it's the door that controls the temps, I believe

Sounds like you need outside air pressure to open the door and allow heat, which means that at standstill the door is closed regardless of your control settings

How fast does the heat start back when you start moving and at what speeds? Not sure that will contribute to a solution but

seeya

Must be a C4 thing.. Mine does it too... Got worse after I changed the water pump and did the TB bypass..

That door works off of vacume.
Try this not moveing but raise the rpm in neutral.If that helps then it could be a vacume leak.
The door actuator has a vacume diaphram mabey a small hole in it.

That was my problem.

as said above youre probably low on coolant or have a big bubble in your system. Could be the heater control valve too. It has to be one of the two.

added some coolant and that did not solve the problem...
how do I change the heater valve?

How much coolant did you add? Was the radiator low when you opened the cap?

One way I fill mine is to start the car, open the cap, and start a slow rev using the throttlebody. When the coolant drops as the revs go up keep adding coolant til full. That will help get most of the air out of the system.

How low was your coolant level/how much did you add?

here is the way I add coolant to make sure its full.

Start the car, make sure its warm and thermostat is open. Open the rad cap and fill it up. Using the throttlebody start a slow steady rev of the motor. When the coolant drops in the radiator fill it up. Do this until adding more revs doesn't really drop the coolant level. The put the cap back on before letting off the throttlebody. That should help get most of the air out of your system.

same problem have wondered but always forgot to post thanks

So you dont think its vacume related?