my heater died on me this morning. i jumped in my 2001 disco this morning and after starting up and letting it warm up i turned on the heater on hi. it was starting to blow warm air when it quit and just started blowing cold air. doesnt matter what temp i put it on it just blows the same cold air now. the fan will change from low to hi speeds and the temp will go from lo to hi but with no change in the air temp comming out. and now it wont blow warm air at all. anyone have this issue before or know what to do to fix the problem?

 

Assuming your coolant level is correct: Either the heater core is clogged with a "leak seal" product or other crud, or for some reason your actuator motor is toggling air flow away from the heater core.

Most likely the heater core is clogged. Disconnect both heater hoses going to the heater core, and see if you get any flow through core with a garden hose.

 

Also, this can be an engine overheat producer. Low coolant and you won't have heat, and core blocked is same - but that also changes how fast hot coolant reaches the sample holes on the thermostat to make it open. The system is designed so that coolant must flow thru heater core whenever engine is running.

Here' a map:

 

Ok I am having sort of the same problem when you start the car and turn the heater on and let it idle say while in the store you come back out and the car is blowing cold air but as soon as you start driving it the heat kicks back in as though it had never went to cold blows as hot as it should have been the whole time. Any Ideas???

 

Coolant level low, heater core reduced, etc. Water circulates from block to heater and back, even whne thermostat is closed. No valve. So should not drop in temp unless something else wrong. If low, when main thermostat open, the flow all goes there. See page from RAVE

 

Quit starting your truck and letting it idle till its warm enough for you, turn on your seat heater when you get in a cold truck, start the engine and go, other wise you are letting your engine run full rich and loading up your oil with crap.