Hot air out of defrost vents when moving.

[Rust-O-Matic]

Hi guys, I need to look through my manual a little closer, but thought I would get your opinions as well. My '66 has (what I believe to be) the deluxe heater and factory AC (compressor, etc. all missing). The heater levers are all broken off, and one on the right is stuck, but the others seem to still operate their cables. The AC knobs are all there, and appear to move their cables as well.

I recently got the truck licensed and noticed after driving a few miles it gets pretty warm in the cab. This weekend I played around with it a little bit, and noticed at highway speed there is hot air blowing out of the driver side defrost vent. It doesn't matter if the lever is set to floor or defrost, it still blasts out of the defrost vent. I tried pulling the "recirculate" AC knob, which sounds like it is opening and closing a door, but it doesn't seem to make any noticeable difference.

To clarify, the blower fan doesn't appear to be working at all. It's on my list of crap to troubleshoot soon, too. The heat is only coming out of the defrost vent when the truck is moving, which makes me think something is stuck open and allowing outside air through the heater core. I'm not exactly sure where to look though. Any ideas?

[PGSigns]

A deluxe heater has a door in it to allow air in from the cowl. You need to see if it is open or closed. The reason most the time for air out just one side of the defrost is the tube is bad going to the other one. I put a heater control valve on mine to stop the water flow on warm days and use a choke cable under the dash to operate it. Really slows the hot air when you done need it and allows me to bring in fresh air through the dash.
Jimmy

[Rust-O-Matic]

Yeah I wondered if the other vent hose is just plugged up or disconnected. Any idea where the door is located? Do I need to take the cowl back off and look for it down through there? Or is this something that can be seen from under the dash? I just had the cowl off, replacing wiper parts. Wish I would have thought about the heater while I was under there.

And is this door we are talking about separate from the A/C "Recirculate" knob? The diagram in the manual appears to show two doors, and I'm not sure what controls them yet. Sorry if these are dumb questions, but I'm totally unfamiliar with the heater setup in this thing. I considered just putting a valve in the hose and shutting the heater core off for now, but with winter coming up I'd kinda like to get it working correctly.

[PGSigns]

I'll get a pic of how I did my heater control valve. Door is at the top of the heater box right at the firewall.
Jimmy

[Rust-O-Matic]

Cool, thanks man.

[Rust-O-Matic]

I finally tore into the heater issue last night, and removed the entire box from the firewall. I have a couple more questions.

The cable attached to the lever labled "heat" on the dash opens and closes a flap above the heater core that looks like it lets air in from the cowl area. How exactly does this change the level of heat entering the cab? I can't quite wrap my head around which way the air flows through the heater box assembly. When that flap is not allowing cowl air in, where does the air come from?

Also, can anyone tell me what the door is for next to the blower motor? There's the flap above the core, which I mentioned above. There's another one on the back of the core's box that is attached to the a/c "recirculate" cable, which seems self explanatory. Then there is a third, smaller door down lower, by the blower motor that didn't have a cable attached. It has a spot for a cable, but was unooked. I can't seem to figure out what is supposed to operate this door, or what it's purpose is.

I also have an extra cable dangling under the dash that isnt attached at either end. I don't know if it's related to the door by the blower motor, but there doesn't appear to be a control lever to attach it to. All 3 levers on my dash already have cables attached.

Any input would be great. I can take pics too if that would help.

[lbspd]

In the deluxe the far-right “Air” lever controls the vent door so air can flow from the heater core to the cab and why the instructions tell you it must be open when the fan is on or risk overheating the fan motor.

The “Heat” lever controls the flow of hot water/coolant from the radiator into the heater core.

The dangling cable is likely the “Heat” since most of the replacement heater cores do not come with the flow valve.

[Rust-O-Matic]

Thanks, but the far right lever on my truck (and all the pics I've seen) says "heat" not "air", so I'm not sure I follow what you mean. This "heat" cable currently moves the vent door above the heater core that allows air to enter the heater box from the cowl area.

The middle lever turns the blower fan on and off.

The left "def" lever moves a door inside the big black plastic a/c housing under the dash.

Here's a pic of the door/flap I'm asking about at the end of my last post. It has a spot for a cable to attach, but I don't have anymore unused levers, so I don't know how it's supposed to work.

[lbspd]

My bad, even though your post clearly says your truck is a 66 for some reason I was thinking 63.

Don’t suppose the below assembly drawing helps, I think it’s the right one for a 64-66 but…

[Rust-O-Matic]

Thanks, you just reminded me to look back through the '66 supplement portion of my service manual. I guess if all else fails, read the manual.

If I understand this correctly, it looks like the middle heater control lever labeled "air/fan" is not only supposed to switch on the blower motor, but also simultaneously pull a cable that opperates the small door near the blower I had asked about. It sounds like that door may be the source of the air flowing through my defrost vents, and the unhooked cable I found is likely what is supposed to be operating it.

I got a new set of heater control levers recently to replace my broken ones, so I'll try to reattach that cable while I'm reassembling it afterward.

Any great ideas on the best way to free up stiff or stuck cables? A couple of mine are sorta hard to slide. Pb blaster and work them in and out a little?

[Captainfab]

I have never seen that in any of the heaters I have worked on or removed in the past 40 years. That must be specific to an A/C equipped truck.

Originally Posted by Rust-O-Matic

Thanks, but the far right lever on my truck (and all the pics I've seen) says "heat" not "air", so I'm not sure I follow what you mean. This "heat" cable currently moves the vent door above the heater core that allows air to enter the heater box from the cowl area.

The middle lever turns the blower fan on and off.

The left "def" lever moves a door inside the big black plastic a/c housing under the dash.

Here's a pic of the door/flap I'm asking about at the end of my last post. It has a spot for a cable to attach, but I don't have anymore unused levers, so I don't know how it's supposed to work.

[Rust-O-Matic]

Which part specifically do you mean Captain? The flap/door I'm pointing at in the pic, or some part of my description of the cable routing?

You seem extremely knowledgeable, and I enjoy reading your posts. I didn't think there was anything on these trucks you had never seen haha.

Originally Posted by Captainfab

I have never seen that in any of the heaters I have worked on or removed in the past 40 years. That must be specific to an A/C equipped truck.