C2 - 1963 AC Question

[Harry S.]

Sitting on top of the interior AC/Heater box is the Vacuum Control Valve. On one side is the vacuum from the carb. When the Vacuum switch is activated (the plunger is released) it terminates the vacuum to the hot water shut off valve and allows hot water into the heater core.

I know this sounds back-wards but the system is designed so that water never flows into the heater core unless you want heat.

I believe my hot water shut off valve is bad because it never closes, with an IR gun it is equally hot on both sides.

I'm trying to determine if my vacuum control valve is good or bad so here is the question. When the plunger is released should I be able to suck any air through the valve? (carb. hose side). I seem to be able to suck air through whether the plunger is in or out.

Thoughts/comments please.............Thanks

[Wayne W.]

Re: C2 - 1963 AC Question

Most likely it is bad, most all of them are, but if I remember correctly, there is a bleed off hole there too.

[Larry M.]

Re: C2 - 1963 AC Question

Sitting on top of the interior AC/Heater box is the Vacuum Control Valve. On one side is the vacuum from the carb. When the Vacuum switch is activated (the plunger is released) it terminates the vacuum to the hot water shut off valve and allows hot water into the heater core.

I know this sounds back-wards but the system is designed so that water never flows into the heater core unless you want heat.

I believe my hot water shut off valve is bad because it never closes, with an IR gun it is equally hot on both sides.

I'm trying to determine if my vacuum control valve is good or bad so here is the question. When the plunger is released should I be able to suck any air through the valve? (carb. hose side). I seem to be able to suck air through whether the plunger is in or out.

Thoughts/comments please.............Thanks

Harry:

Vacuum applied to the original 1963-1967 hot water valve will OPEN the valve and let the hot water through it. No vacuum to the hot water valve will close the valve and prevent hot water flow through the heater.

Later year cars (some of the later C3 cars) hot water valves operated in the reverse to what I stated above: vacuum would close the valve and prevent hot water through the valve to the heater.

The small vacuum switch on the heater box has a special rubber o-ring in it for a seal. This o-ring will often go bad with time (20+ years or so) and stick in one position or another. For your car, if you set things up for heat, there should be vacuum through this switch to the water valve. If you change and want cool air, then there should be no vacuum at the water valve. Doc Rebuild has a write-up on his website on how to repair this o-ring. Also, the "other forum" had an excellent article with part numbers and photos on how to do this repair also. You can also buy a new, reproduction switch from LICS and a few other companies.

On my 1967 factory air car, the vacuum supply comes off the intake manifold, not the carb. Not certain about 1963 car.

Larry

EDIT: In the way of troubleshooting, with the car running and hot water going through the valve and heater, remove the small hose to the hot water valve. See if there is vacuum at this hose. There should be if you selected heat. Also, with this hose removed, the hot water valve should go closed and the heater should cool down. If this water valve remains open with no vacuum source, then the valve is bad. I do not know if the valve can be repaired, you can try. LICS also sells a new, reproduction hot water valve that is very close to the original. Price is $$$.

[Harry S.]

Re: C2 - 1963 AC Question

Larry, I was confused about that also. Based on reading this again and your input, thanks

From the Service Manual:

A significant difference is that in the Corvette Air Conditioning System there is no flow through the heater core until the COOL IN-HOT PULL knob is pulled out. The movement opens the vacuum switch on the air distributor assembly and allows vacuum to be applied to the water valve mounted in the engine compartment, opening the valve. Thus the heater core is unheated until needed, at which time it receives full flow of the engine coolant.

Vacuum opens the hot water valve and lack of vacuum closes it is the way I interpret it. Anyway, my vacuum valve allow vacuum through the valve weather the plunger is in or out, so I guess it is bad.

[Edward J.]

Re: C2 - 1963 AC Question

Harry, If I am reading your post correctly, The vacuum hot water valve is moving the arm in both directions when you push or pull the lever, But the temp is staying the same on both sides? If so the flapper door in valve maybe be gone. I do not know what material the internal door of the valve is made of, but its either plastic or metal, Either way the metal one will rust out and the plastic one will desinigrate with age.

[Harry S.]

Re: C2 - 1963 AC Question

Harry, If I am reading your post correctly, The vacuum hot water valve is moving the arm in both directions when you push or pull the lever, But the temp is staying the same on both sides? If so the flapper door in valve maybe be gone. I do not know what material the internal door of the valve is made of, but its either plastic or metal, Either way the metal one will rust out and the plastic one will desinigrate with age.

Ed, I'm referring to a different part on an AC car. The hot water shutoff valve is added to the Hot water hose, engine side, to stop hot water from entering the heater core on AC cars. If the valve is constantly open then you have a hot heater core warming the cold AC air before it hits the car interior, thus no AC.

[Larry M.]

Re: C2 - 1963 AC Question

Ed, I'm referring to a different part on an AC car. The hot water shutoff valve is added to the Hot water hose, engine side, to stop hot water from entering the heater core on AC cars. If the valve is constantly open then you have a hot heater core warming the cold AC air before it hits the car interior, thus no AC.

Harry:

The heater/AC box also has an internal flapper door that directs the air flow either across the heater core or across the AC evaporator core or across BOTH, depending on whether you want hot or cold or warm dehumidified air. However, in the COLD position this flapper SHOULD prevent any of the cold AC air from flowing across the heater core. Unfortunately over the years, the seals on the flapper do not seal very well anymore. Having the additional hot water shutoff valve insures that whether the flapper door seals or not, when you want maximum cold air, there is no hot water flowing through the heater/AC box.

Sort of a belt and suspenders approach to getting maximum cold air for the times when you want it.

Larry