I have a heating problem that I was unable to find in the threads, maybe somebody has a solution. I have a 1999 Seville STS with 111,000 miles that I bought about 10 months ago, after it had been mostly sitting for about six years. The problem: After the initial startup and the engine warms, I have no heat until I shut down and then restart the engine. The AC works normally, but no combination of the temperature controls will generate any hot air until I restart. I have already replaced the radiator, thermostat and coolant and recharged the AC but the problem predates those actions. The purge line is clear and flows freely and there are no DTC or OBD II codes. The ambient air temperature sensor seems to be working correctly.
In summary: Start engine, reach operating temperature, AC but no heat, restart engine, great heat. Any assistance will be appreciated. Thanks!