doug holt

Hello, my heater blows cold air. Will not get hot at all. Put new thermostat in. Tempeture gauge reads normal reading. Heater hose gets hot going to vaulve. Could vaulve be bad? The vaulve that is inline the heater hose. Any info. Would be appreciated. Thank you Doug

jerseybud

I'll assume you have AC if you have a heater valve. Valve should move when you press max cool button from the off position on your hvac controls.
The entire system is controlled by vacuum so check that first, section by section. The diaphragms on top of the heater core may leak and then the heater doors will bleed off the warm air.
Could be a blocked heater core, esp if original
Does the fan work? all 3 speeds?

doug holt

Yes all three speeds work on the fan I will check the vacum and check make sure heater core is not blocked thank you for your reply

j_martin

Lay a hand on each of the 2 pipes going into the heater through the fire wall. If one is colder than the other, or both are cold, then either the valve, or the heater core is blocked. If they are both hot, then a damper in the heater box is stuck in the AC position.

doug holt

Ok I believe it may be the vaulve you put one hand in front of it on the pipe it's warm on the other side it is not hot at all How many dampers are there in the heater box? Thank you for your replies very much appreciated

j_martin

It could be the valve or the heater core. Observe the valve. You should be able to see it throw. You could replace it with a hose splice. If the valve works or is eliminated, then the heater core is plugged.

The damper of concern here steers the air through the heater core or the evaporator. I believe it is manually operated by the lever on the controls.
I think there's one for the dash vents, and one for defrosters also, vacuum operated.

Jim5870

I have had cases when the little air doors inside the HVAC box seize up.
The door is on a steel shaft hinge and they seize up to the case.