A/C but no heat

[Jaybird81]

1981 C10 A/C works but heater does not. Climate control unit is new. Where do I start?

 

[mattsk8]

I assume the blower is working when it's set to heat since you said the AC works? I would first check the coolant level. If coolant is full and temp on your temp gauge is good, possibly a plugged heater core.

 

[fast 99]

are heater hoses hot, temperature difference between the 2? Temp split around 20-25 degrees indicates a plugged core, no or low flow. Check after warm and heater has been operating. When coolant was added did you bleed air out?

 

[Ricko1966]

Because he says he has a new heater control, I'd be checking blend door operation

 

[Jaybird81]

3/4 of a gallon low on coolant. See if that helps…

 

[Jaybird81]

So I’m checking the routing of the hoses. And I think they are on backwards the top hose coming out of the firewall from the heater core should go to the radiator and the bottom hose coming out of the firewall should go to the engine, correct? Mine are the opposite.

 

[Steelbuddha]

So I’m checking the routing of the hoses. And I think they are on backwards the top hose coming out of the firewall from the heater core should go to the radiator and the bottom hose coming out of the firewall should go to the engine, correct? Mine are the opposite.

The heater core isn't directional, so which hose is on the top and which is on the bottom shouldn't make any difference as long as there's coolant flowing through it. (Which it sounds like there might not be.)