Hidden Heater Control Valve

[BruiserOutdoors]

I took these photos last year at the Northwest Bronco Roundup. I really like how clean the routing is on the heater hose lines. There is no heater control valve. Is it hidden behind the dash do you think? I hate the look of the bulky heater control valves.

What would be the complications of hiding the heater control valve behind the dash? Doesn't the heater box poke thru the firewall allowing no way to put a valve behind the dash?

 

[Steve83]

What makes you think there's a hidden valve? I see no valve. Later Broncos are built with no valve, so that's probably what's going on there.

 

[BruiserOutdoors]

What makes you think there's a hidden valve? I see no valve. Later Broncos are built with no valve, so that's probably what's going on there.

well I figured a valve was a necessity. is it not? if it is not, why would anybody ever add one back? Doesn't the valve allow the heater to be on or off?

Clearly I am not familiar with a heater system and how it functions.

 

[DirtDonk]

You are correct that on a stock early bronco system you can’t hide it. You either leave it out (hot coolant flowing all the time) or you have one under the hood.
There are variations of the under hood theme, but there has to be a valve on a stock system if you want to shut off the hot stuff from getting into the cabin.
Now, if you have figured out how to completely stop any air from flowing through the system, you can leave the valve out.
But most of us have not figured that out yet.

Or with something where the valve is built into the mechanism under the dash, such as aftermarket air conditioning, then you can have a hidden valve.
Maybe that’s what’s going on here, but if it is, they figured out a way to make the hose nipples come out of the original holes.
If that’s the case, they should’ve spent some extra engineering time on moving the hose nipples for better hose routing!

 

[BruiserOutdoors]

You are correct that on a stock early bronco system you can’t hide it. You either leave it out (hot coolant flowing all the time) or you have one under the hood.
There are variations of the under hood theme, but there has to be a valve on a stock system if you want to shut off the hot stuff from getting into the cabin.
Now, if you have figured out how to completely stop any air from flowing through the system, you can leave the valve out.
But most of us have not figured that out yet.

Or with something where the valve is built into the mechanism under the dash, such as aftermarket air conditioning, then you can have a hidden valve.
Maybe that’s what’s going on here, but if it is, they figured out a way to make the hose nipples come out of the original holes.
If that’s the case, they should’ve spent some extra engineering time on moving the hose nipples for better hose routing!

so by eliminating the valve, hot coolant will always flow into the cabin and therefore hot air will flow out the heater? even with the heater fan off?


in other words, what is the downside of losing the valve?

 

[Steve83]

Ford designs vehicle cabins' aerodynamics so that, if the vehicle is moving, air flows through the cab, regardless of HVAC settings or other options. On later trucks, there's a door that causes air to bypass the heater core, so it can always have coolant flowing through. But in the eB stock system, air always flows through the heater core, so the valve shuts off the flow of coolant, meaning the stagnant coolant loses heat, letting the air get cool (ambient). You should have gotten under-dash pics of that truck, to figure out how its HVAC works.

This & the NEXT pages show the eB system:

(click this text)


This is the later ('80-96) configuration:

(click this text)

 

[ba123]

Did it have Vintage Air AC? If so, it’s easy to put inside the cab, under the dash and it’s small. I suppose yo7 could use that valve even without vintage air and have it electronically controlled, no reason you’d have to have that buoy thing with the oil cord attached to it.

Lots have put it there and I’m about to do the same. I’m also doing something similar with my heat and AC lines, but can’t decide exactly where I want them.

 

[Broncobowsher]

That looks like a stock heater. And no control valve.
The short answer, it is installed wrong. Appearance over function.
I bet the cabin runs a little warm. Hopefully the "pull for heat" flap is sealed up really well.

 

[Steve83]

There is no such flap. Pull-for-Heat only operates the valve, which is missing in that truck. If there were a flap, it would block all airflow because all the air always passes through the heater core.

 

[BruiserOutdoors]

Did it have Vintage Air AC? If so, it’s easy to put inside the cab, under the dash and it’s small. I suppose yo7 could use that valve even without vintage air and have it electronically controlled, no reason you’d have to have that buoy thing with the oil cord attached to it.

Lots have put it there and I’m about to do the same. I’m also doing something similar with my heat and AC lines, but can’t decide exactly where I want them.

no vintage air that I see. Very clean build.

 

[ba123]

Yeah looks like they wanted the stock look without the ugliness of the valve.

Some like it hot.

 

[DirtDonk]

There is no such flap. Pull-for-Heat only operates the valve, which is missing in that truck. If there were a flap, it would block all airflow because all the air always passes through the heater core.

Not correct Steve.
The “TEMP” knob opens and closes the valve.
The “Pull for heat“ knob opens and closes the damper door/flapper valve that blocks off airflow through the heater core.
Or at least it attempts to block flow, since they are rarely very well sealed.

 

[DirtDonk]

With this setup the driver can control two vents. The door by the driver’s leg and the air inlet from the passenger side through the heater plenum.
Assuming that the temperature valve is closing sufficiently, you can get some more cooling air from the outside.

 

[Steve83]

The “TEMP” knob opens and closes the valve.
The “Pull for heat“ knob opens and closes the damper door/flapper valve that blocks off airflow through the heater core.

I really want to understand this. Do you have a better diagram or photos of the blower box internals than these?

(click this text)


(click this text)


Both of them show both flaps on the left (driver's) side of the blower, and the heater core without any flap on the right side. Flap 18A478 looks to switch between floor & defrost by pulling/pushing the left knob on 18578, but I can't tell & have forgotten what 18B254 does when the right knob 18552 is pushed/pulled. The valve is controlled by pushing/pulling the center knob 18518.

I know the knobs often get moved around during repairs/restorations, and that their labels might also get swapped, so these positions only apply to the original layout. But Pull For Heat should be the center knob since that's what opens the coolant valve.

 

[DirtDonk]

Funny, but I was mentally under the impression (faded memory) that the Pull-For-Heat damper door was between the heater core and the fan motor/squirrel cage.
Looks from the diagram like it’s actually after the fan in the squirrel cage and simply opens and closes the left half of the plenum that contains the outlets to the floor and defrost duct, to the right half that contains the heater core.
You’re correct that there is nothing between the heater core and the fresh air inlet on the passenger kick panel, but there is a complete block between the heater core (and apparently the fan motor) and the outlets in the cabin.

The pull for heat and the fan on off/high low switch are integrated. Pulling the knob for heat doesn’t change temperature or quantity of coolant running through the core. Pull for heat opens and closes a damper door simply to allow the heated air into the plenum, floor register or defroster ducts.

So, if you just turn the fan on without pulling the cable, no air blows into the cabin. Pulling the knob, even without the fan, allows air into the cabin once you are driving, and the motion of air over the hood goes into the passenger side ducting.
Just like a standard vent.

 

[DirtDonk]

But no, I don’t think I have a better diagram. I’ve seen some pretty good ones in the big, thick Ford manuals that show everything in locations, but it’s also pretty close to the one you posted. If not the same.

 

[ba123]

I’m just watching this thread for interest and it’s been so many years since I’ve looked at any of this, but doesn’t the pull for heat control open up the valve to let the hot water from the engine go to the heater core?

I just searched and found someone posted this a while back:
Far right controls hot water moving through you're heater core. Pulled out for heat. Middle control fan off hi n low,pulled out to open up air passage from heater core. Left knob pulled out is defrost,pushed in is heat to the feet.

 

[DirtDonk]

That is the same thing I am saying. Just without quoting of the wording on each control knob.
The TEMP does only one thing. That is for increasing or decreasing the actual temperature. And the only thing that does that, because we don’t have a blend door type system, is the heater control valve under the hood.
The high/low/pull for heat opens up the air passage from the heater core.
Just as you quoted above from another thread.

 

[Steve83]

I'm still fuzzy... I don't understand the purpose of the "temperature" door 18B254, or how it could possibly affect the air temperature.

I forgot I had this: left is always Defrost (door, 18A478 push/pull); center Heater (valve, push/pull)/Fan (motor speed, rotate); right Temperature (door 18B254, push/pull).

(click this text)

 

[bigmuddy]

I'm still fuzzy... I don't understand the purpose of the "temperature" door 18B254, or how it could possibly affect the air temperature.

I forgot I had this: left is always Defrost (door, 18A478 push/pull); center Heater (valve, push/pull)/Fan (motor speed, rotate); right Temperature (door 18B254, push/pull).

(click this text)

I believe the right knob for temp just modulates the door/flap allowing hot air into the cabin, while the middle knob helps to modulate how much hot fluid is allowed into the heater core.