ledfordwc

I've put two thermostats in it and the heat just works every once in a while, most of the time ot just blows out cold air, then out of the blue it'll get hot then it'll just go cold again, is it that its a bad vacuum line or something else simple?

sylver91

Have you checked the vent door actuator? It might be stuck and only letting the cold air come in and not around the heater core. Its on the firewall on the far left. If the vacuum hose is brittle may be something to look at.

wde3477

Verify the proper coolant level - air pockets wreak havoc on heater output.
Verify the engine is reaching target temperature.
Verify both heater hoses to the heater core are hot - hoses not pinched, tied into the proper points off the block, etc.
Verify the temperature blend door is actuating properly. Mine is cable controlled, had to tweak the cable clamp to get full door sealing. If there were a problem with the airflow diverting dampers - should still be getting heat out somewhere.
Has the system been flushed recently - a clogged heater core, or a cheapie heater core will not have good output.