[clutch492]

I know exactly what the problem is, and it is a VERY simple fix. I have had a cavalier and now a sunbird with this very problem.

Here is what you do: remove the blower motor. Reach in with your hand and feel the heater core. What you will find is a thick coating of black stuff covering the entire heater core. Scrape as much of this stuff off with your fingers and then use a vacuum to suck the rest out of the heater box. Now, take an air hose and a blow nozzle (with an L shaped end) and blow through the heater core to get the last of the black crap out of the fins.

What this is, is mold and dirt that has accumulated on the heater core.

I have had 2 convertibles and they are cold cars if the heater doesn't work. I know what you guys are going through. THIS WILL FIX YOUR CAR.