C2 with air and vacuum leaks

[Randy S.]

C2's with C60 air have a vacuum controlled hot water valve controlled by the vacuum switch behind the glove box. My understanding is the water valve is normally closed. Pulling the heater plunger on the dash opens the vacuum switch sending vacuum to the water valve and opening it allowing hot water to the heater. The vacuum switch has a bleed hole to bleed off vacuum allowing the water valve to close again when the heater is turned off.

Why doesn't the vacuum switch with bleed hole act as a vacuum leak?

Randy

[Mike M.]

Re: C2 with air and vacuum leaks

randy: been a while since i worked on my c-2's with c-60 but as i recall, the valve positioned in the heater hoses is open at all times except when the air cond is turned on. mike

[Wayne M.]

Re: C2 with air and vacuum leaks

Randy -- your description of the operation is correct; ie. the hot water valve is closed when no vacuum is applied (no flow through the heater core) and opens when the "COOL IN - HOT PULL" knob/cable (upper RH side of clock) is pulled. With the knob fully in, the temp valve lever on the under-dash duct assembly fully depresses the piston of the vacuum switch. In the interests of science, I have removed my '65 vacuum valve and now have it in front of me. I believe it works as follows:

The valve body has 2 obvious ports (big I.D. hose nipple, vac input source from manifold, and the small hose I.D. nipple for output vac signal to the heater control valve). What you DON'T see when this valve is mounted, is the bleed hole [0.045" dia] on the underside. So piston blocks vac from entering valve body when depressed (and bleed hole not exposed -- theoretically, no vac leaks). Now examine the other extreme, when the "hot" dash knob is pulled out sufficiently (less than 1/4" is all that's required) to fully extend the vac valve plunger. The source vac then feeds directly to the outlet hose, and the bleed hole is again covered by the internal piston. It is during the INTERMEDIATE travel positions of the piston that expose the bleed hole so that the heater control valve will close when the dash knob is pushed in. The design also exposes the bleed hole when you turn ON the heat (ie pull the knob), so there is a vacuum "leak" at this instant, but this is only for a fraction of a second, until the piston is fully released.

There are adjustment directions in the AIM to ensure this piston is seated when the cable is pushed in.

Now what I would like to know is if there are rubber/synthetic internals on the valve, as I'd like to give it squirts of carb cleaner.

[Page C.]

Re: C2 with air and vacuum leaks

Hi Wayne,
I have a Dr. Rebuild catalog that tells you how to repair this brass valve. It's on page 55 of the volume 27 catalog. The switch has a rubber "O" ring inside.
Also a 1965 Corvette #23551 (327/365 air car) you gave me some info on long ago is on E bay #4517007752
Page Campbell

[Randy S.]

Re: C2 with air and vacuum leaks

Wayne,
Thanks for the detailed explaination. I hope you didn't tear into your glovebox just to answer my question :-).

An intermittent bleed hole explains it. I can sleep now.

Randy

[Wayne M.]

Thanks for the link, Page ...

... unfortunately, the last Dr. Rebuild catalog I have is Vol 23 (I must get out to more swap meets). Do you know if it's on-line ? (in pdf or html).

That '65 # 23551 could be the last St.Louis body coupe of that model year. The description doesn't mention it, but one of the previous owners told me that the script "LAST Job" is scrawled in crayon under the jute of the interior rear compartment.

[Geoff C.]

http://www.docrebuild.com/dr-r-web/ac-50tip.HTML *NM*

[Wayne M.]

Thx. Doc -- Great catalog, plus all these tips *NM*