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Cab Heater Question

Unread postby RobC on Fri Aug 21, 2015 11:35 am

dug into my inoperable heater unit under the passenger dash.

I have power to the fuse panel but the fan motor won't blow. Probably going to have to remove the unit for diagnosis maybe a new fan motor.

These things are a b#tch to work on. You can tell the exit air hoses were installed on the unit BEFORE it was installed as the hose clamp adjustment screw heads are facing forward (where you can't get to them)!!

Question:
The dash controls have a "Highway Temp" knob that looks like it opens/closes a valve located in-line with the coolant lines to the heater that allows/blocks coolant from going to the heater unit.

I assume that "highway Temp" means you are flying along the hiway with lots of air going through the radiator with no need for additional cooling vs stuck in traffic no air flow and higher temps. When open, coolant is allowed to flow to the heater which acts as a second radiator in overheating conditions.

I used to regulate my old Subaru (motor fan cooled) temps by cranking the heat and the fan which basically made a second radiator in the cab roasting me and my passengers. As soon as I did it the temp gauge would come right down 20 or 30 degrees.

My valve is stuck but I wanted to figure out the system before I unhook all the lines and pull the whole unit out.

RobC
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Re: Cab Heater Question

Unread postby RobC on Fri Aug 21, 2015 11:49 am

Couldn't see the bump topic button so am trying the backdoor to get my heater questions on the main page.

See original post above.

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Re: Cab Heater Question

Unread postby Acesneights on Fri Aug 21, 2015 3:36 pm

Mine has a city/highway temp but it's for the A/C.
Can you post a pic of what you have ?
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1974 Travco 220 Parts unit
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Re: Cab Heater Question

Unread postby RobC on Mon Aug 24, 2015 11:45 am

Here are a couple pictures of what looks like a gate valve in line with the heater supply line.

these shots are looking up from the passenger floor. Heater box is on the upper right, Red hose is supply or return line from radiator

Valve looks like it is half open. The corrugated rubber hose is the passenger heater vent house. This is the one with the hose clamp screw on the front where I can't get to it.

I can grind it off but not much design thought went into these rigs.

Any ideas as to why it is there and why they called it Highway Temp on the dash knob would be appreciated.

Cheers. RobC

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Re: Cab Heater Question

Unread postby Acesneights on Mon Aug 24, 2015 4:30 pm

Can you show me a picture of the controls on your dash ? On mine that valve is controlled by a push pull cable(kinda like a choke cable).
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Re: Cab Heater Question

Unread postby RobC on Tue Aug 25, 2015 12:09 pm

Didn't have time for a pic but Yes Aces I have the same push pull type knob on the center console top right next to the motor control.

I think I have no choice but to pull the whole unit and get it running and see what lurks behind the heater....

There is a black house that goes up toward the AC unit then back down through the floor to the engine compartment to nowhere. The AC Unit is not hooked up and the compressor is gone on the motor.
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Re: Cab Heater Question

Unread postby 77Travco on Tue Aug 25, 2015 2:36 pm

I know that when you pull the knobs out you get heat. There's an owners manual around here somewhere....
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Re: Cab Heater Question

Unread postby Acesneights on Tue Aug 25, 2015 6:33 pm

If you need any pics of how the compressor mounts let me know. Most of these had Mark IV kits installed by people like my father. Mine has a Sanden compressor conversion from the original Tecumseh. If you are going to convert to R134a Vintage air sells everything you'll need as well as replacement vents for the dash.
The heater comes out pretty easily. I had my core redone at a radiator shop. Was around 100$ for a recore.
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Re: Cab Heater Question

Unread postby RobC on Wed Aug 26, 2015 1:12 pm

Thanks.

77: that makes sense as it seems the gate valve shuts off the supply line to the heater. I have been doing exterior work getting ready for paint before the rain comes here in the NW so interior has taken a back seat of late.

Rob
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Re: Cab Heater Question

Unread postby 77Travco on Wed Aug 26, 2015 3:45 pm

RobC wrote:Thanks.

77: that makes sense as it seems the gate valve shuts off the supply line to the heater. I have been doing exterior work getting ready for paint before the rain comes here in the NW so interior has taken a back seat of late.

Rob

Be sure to post up some paint pics!
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