1994 Chevy Caprice

This could be anything from your heater shut off valve is stuck, you have a clogged heater core, to you have air in the system due to a blown head gasket.

To check the heater shut off valve, allow your engine to run until hot, then place your heater controls on full hot. Locate you valve on a hose going into the fire wall then touch both hoses going in and out of the valve. If one is hot and the other isn't, then the valve is shot.

Next, look into either your radiator or surge tank. If you have stuff floating around in your anti-freeze, then you could possibly have a clogged heater core. Flush your system and recheck.

To check for a blown head gasket, open the cap on your surge tank. Start your motor and place your heater controls on full hot. While you rev the motor to at least 1,500 r.P.M.'S, look inside the surge tank. If there are large air bubbles, then your gasket is blown. Time for a new motor.