Heater problems

[nelstomlinson]

When the temps hit -40, I realized that my heater wasn't working. '89 crewcab, XLT model with factory air.

The little vacuum actuator which shuts off the air through the heater core wasn't getting vacuum, wasn't opening. I have zip-tied it open now and I'm again getting a little heat, so that's OK for now.

The bigger problem is that the fan motor only has one speed, and that's slow! I can't get enough hot air and the windows and windshield ice up on the inside. I suspect it's the speed control resistors. Where are they? Behind the dash?

 

[catbird7]

Should be under the hood, mounted in heater box. LMC usually has them. You can likely find an illustration on their website.

 

[nelstomlinson]

The fan switch is definitely cooked, and the local parts store will have one for me tomorrow. LMC does have an illustration of the heater components, but can't really tell where to look for the resistor from that. With any luck the fan switch will be the only thing I have to replace.

From the LMC diagram, it looks as if the flappers in the ducts are controlled by the vacuum, and from looking inside the dash, it looks as if there is a cable which controls the flow of water through the heater core.
Edited to add:
I found the resistors. They are indeed under the hood, inside the heater box, below and inboard of the blower motor. The resistors are good, so just changing the burned up switch should be all it takes.

 

[mexicanjoe]

My 89 extended cab truck has heater hoses that run unimpeded from the passenger side head to the front of the motor: no shut off valve!?!?!

 

[Old Goat]

My 86 has the Heater Hoses connect to the Heater Core at the Fire Wall. No Coolant valve/Cable. Maybe it was changed in later trucks?

One thing that can be a big problem, is the Hinge on the Blend door breaks and the cold out side air cannot be shut off.
Here is a thread and also good pictures of the guts of the Heat/AC Box.

How to Repair the AC Vent Door Hinge - Ford Truck Enthusiasts Forums

'80-'86 HOWTO's - How to Repair the AC Vent Door Hinge - If your '80-86 Ford truck has factory air, you can expect the following failure to happen at some unspecified time. Your windshield will fog over on the inside, and when you select Defrost and turn up the fan, practically all the air blows...

www.ford-trucks.com

This thread may be useful, but truck years before yours.

HVAC Systems

Illustrations and part numbers for the heaters and air conditioning systems for the Bullnose (1980 - 86) Ford trucks.

www.garysgaragemahal.com

Another one I saved.

Heater help/diagnostics needed - Ford Truck Enthusiasts Forums

1980 - 1986 Bullnose F100, F150 & Larger F-Series Trucks - Heater help/diagnostics needed - Hi, This fall I replaced the heater core so that I would be ready for this winter (old one was leaking), but something isn't quite right. Heater blower runs fine, and all dashpots operate, but I'm not...

www.ford-trucks.com

I doubt but dont`t know for sure, but I doubt Ford changed too much in the way the Heater/AC box was designed from 80 - 94 or? Maybe the front controls.

Hope this helps.


Goat