Arkyvette

I was wondering if the HVAC valve that shuts off the heater core under the hood is normally open with the controls off? My car obviously was because the heat coming out of the vents was unbearable. I ran a bubba vac line to the shutoff valve and the heat is off! I am thinking its my HVAC control head that's the cause here (nothing about it seems to work) unless its supposed to work this way.

MelWff

I would think if the temperature control is set for cold it should send a vacuum signal to close the valve regardless of other control settings.

Arkyvette

I was just wondering what it defaulted to in "off" In my Fords the core only shuts off when using "max AC"

74 LS4-454

That valve is controlled by the temperature lever. When at the "Cold" position, it is off regardless of what the other settings are at. As you move the lever off of the "Cold" positon towards the "Hot" position, it opens the valve accordinly. The more towads "Hot", the more open the valve is with more hot air.

There is a cable that operates that valve from the lever mentioned. If it is not positioned correctly under your console, it will get hung up and not fit into the sleeve, therfore throwing off your adjustment for said valve. Look right under the heater box on the passenger side interior, and you can see the cable operate the valve when moving that lever. The end of that cable may also be out of adjustment.

Easy Mike

Don't quote me on this, but I believe the valve is closed until you say you want warm air.

Arkyvette

I have driven it two days now with the water valve hooked straight to vacuum and I have had a drastic reduction in cabin heat. Its like a different car. I need to get into my HVAC sooner or later though. I have ducts missing and things look messed with under the dash. Its good enough for a t top summer though!

74 LS4-454

If you decide to insulate the floor, you will even notice a bigger difference, best thing I've done to the 82

EmNash

On the 82 the vacum switch is behind the glove box insert. It has a cable that runs to the temp control slide. When the slide is all the way to the left in the cold position it sends vacum to the valve, closing it. This switch is adjustable with elongated mounting holes.

Arkyvette

Good info. My temp slider is a limp noodle, so probably not hooked up, hence being stuck on hot. Thanks!