A/C Heat help

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Joined
Sep 27, 2022
Messages
436
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Location
Tennessee
My Car
Green on green 72 Mach 1
Trying to figure out how the heat works on a A/C equipped car.
I have basically a whole new system, new heater core, new heater A/C box, new water valve vacuum motor. I have the hose off the block with the valve on the heater core tube to the right and the valve is installed with the arrow pointing towards the firewall. The hose coming off the water pump on the heater core tube to the left like what I feel is correct.
Before I installed the water valve vacuum motor I noticed you have to have the diaphragm pulled in like it would be with vacuum applied to it for water to flow. Am I correct?
What is confusing is the water valve switch attached the the hear core box. Does it send vacuum to the water valve when the temp control arm is in the cold position ( pushing on the switch plunger) or in the warm position not pushing on the switch plunger?
With the car fully warmed up and idling and trying to get heat on in the car it seems like I have the temp set on cold and the heat A/C selector in fresh or A/C to get vacuum to the water valve.
Any insight would be greatly appreciated
Thanks
 
Last edited:
The valve is to shut off the hot water flow to the core when the temp selector is in the Cold position. The cable end pushes on the vacuum switch on the box, which opens and applies vacuum to close the valve. IIRC, there are normally open and normally closed water valves. Yours should be open with no vacuum.

There's a diagram in the shop manual that shows where vacuum is applied in each position of the control.
 
The valve is to shut off the hot water flow to the core when the temp selector is in the Cold position. The cable end pushes on the vacuum switch on the box, which opens and applies vacuum to close the valve. IIRC, there are normally open and normally closed water valves. Yours should be open with no vacuum.

There's a diagram in the shop manual that shows where vacuum is applied in each position of the control.
Thanks that is what I was thinking. It bums me out because now I have anti freeze in the line and I’ll have to try to not make a mess with swapping it out.
Would you know of a correct one.
I’m 99.9 percent mine is normally closed.
Thanks
 
Here is the diagram out of the 73 shop manual. As mentioned already the valve in the engine compartment should be normally open. Vacuum should close it when the temp lever is moved all the way to cool. The temp control cable connects to a pivoting arm, the arm pushing the water valve vacuum switch open letting vacuum reach the valve in the engine compartment and closing it. The cable needs to be adjusted correctly to do this via the clamp near its end. With the engine running you should be able to see the valve in the engine compartment cycle from open to closed and visa versa when the temperature control lever is moved to cool and away from cool. This assumes the cable is adjusted correctly and the vacuum system is connected correctly and functioning as it should.
 

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