2004 toyota celica will not blow hot air for twenty minutes

Have you checked the engine temperature when the gauge shows fully high if it is true message and not lying and the problem is the temperature gauge? Since this happened stop the car open the bonnet touch the radiator hoses and even with off running engine touch the vents of the radiator to all surface and see it the temperature is everywhere the same.

you might have a problem with your waterpump. you should ask a mechanic to check the waterpressure in the coolingsystem.

If it is blowing cold air, that means the coolant level is low, the heater core has no coolant in it. Sounds like a head gasket is leaking.

we have a 2004 passat with the same problem. after many different attempts. what we did was. drain the heater core, blow air through the system and then put a mild solvent in the system and let it set for about 20 minutes. flush the system and refill with coolant. now our heater burns us out. use low air pressure and be very carefull. heater core was full of junk that came out after we flushed with solvent.

If no heat you need to check out the valve and/or linkage that allows hot coolant to enter into the heater core. Re the lights you need to get a schematic that gives you the necessary data re hookup so you can track and correct the light issue. I would think it is the switch activated when you put the car in reverse.

the a-c and heater run on 2 different systems the heater needs coolant going thru the heater core to make heat by blowing air through it and the a-c uses it's own sealed system to cool the air so if you have no heat / it has nothing to do with the a-c working or not . first thing you do is check the cooling system like rad and coolant levels . you will have heater core hoses running from the engine to the firewall going to the heatercore . grab the heater core hose and feel if it's hot . if your hoses are hot then the heater core is bad or the blending doors are stuck .

problem could be a bad water pump.

nothing try back flushing heater core, they clog up due to litle water preasure,you might want to flush cooling system if you already havent, hope this hleps.

Yes, those are the hoses that go to the heater core. Just wondering, you didn't say that air is blowing, is it? You also have other components that "decide" your heat into the cabin of the car. What were the symptoms leading up to you deciding to change the thermostat.

Sounds like your heater coil could be clogged. Its a small radiator like device that hot coolant is pumped through to heat the cabin. its very small so clogging is pretty likely.