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Just curious: 70's Ford truck heater air intake source?

Does the heater’s air intake come from outside the cab, or from the inside; i.e. the heater air is just recirculated? If it comes from the outside, where does the air exit back to the outside?

George.

Shouldn’t this topic be in the General Discussion forum?

And not in the Maintenance/Repairs forum?

Tester

Don’t know, but suspect it recirculates.
Some vehicles vented trough the doors. Mid 60s T-Birds had a vent behind the rear window that could be opened or closed via a lever on the console. The last Studebakers vented through the trunk out grills in the tail lights.

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Don’t know whether this is a GD or MR topic. I have no objection if the moderator wants to place it in GD.

George . . .

Are you just asking out of curiosity . . . ?!

Or does your 1974 Ford truck have a problem?

If it has a problem, why don’t you just say so, and maybe somebody will try to help you

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No problem, just curious how it works.

Somewhere back in the 70s (and I’ve long forgotten) the Feds passed a regulation which stated that a vehicle without A/C cannot be manufactured where the fresh air intake can be cut off. What that year was I do not remember. Maybe this applies…or not.

Does your truck have a grate across the the area of the wipers? That would be the intake for the HVAC system.

Yeah, it has grates both right and left under the windshield. The one of the left, where it enters the cab, there’s a door that can be opened or closed. The one on the right appears to head toward the heater, but hard to tell for sure. I’m guessing the heater inlet source is fresh air from the outside and they didn’t worry about where the air would exit, as there’s plenty of places for air to leak out here and there.

Interesting question. I do not recall ever looking for it on my 71 but I would be dang surprised if it was inside the cab!

I would bet that the fresh air for the heater comes in from the grating under the windshield. By the 1970s, I don’t believe any vehicle had a heater that only recirculated the air in the cabin. The last vehicle that had a recirculating heater as standard equipment was the 1957-58 Studebaker Scotsman.
The first heating system that brought in fresh air from the outside was invented by Niel Eric Wahlberg, an engineer for Nash Motor Company. He found that by bringing in the outside air, it pressurized the cabin. With a recirculating heater, there was negative pressure and the cold air would infiltrate the cabin.
One other tidbit:. Buick used to bring air in by an air duct down low in the grill. This allowed exhaust fumes to be picked up from the car ahead. One motorist actually died from carbon monoxide poisoning while his car was stuck in a traffic jam and the fumes from the car in front were inducted into the cabin of his car.

Not sure about your truck, but it probably just leaks out of the many places it can find a path outside…most likely your cowl and the relatively leaky cab of the truck. I have seen hidden vents in cars behind the rear seats…venting into the trunk…and also vents in the trunk as an escape path.

All systems have a clandestine escape route, if they didn’t you wouldn’t get a nice smooth flow of air out of any vents as it has to have an exit. I used to have a hidden vent from a Caprice I think sitting around here somewhere…I was going to take a pic of it…cant find it due to my filing system deficiencies and also because the Maid here quit…or she’s still here buried somewhere, one can never tell.

It looked like a rounded square plastic frame maybe 4x6" with shark gill looking rubber on the inside which made it act not like an open window causing drafts…but more like a membrane that can be pushed through when needed…and closed off when at rest.

George, perhaps some interesting reading for you, especially further down regarding exhaust venting.

https://www.ford-trucks.com/forums/1407421-outside-air-rushing-into-cab-through-center-vent.html

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