Vacuum heater controls

jdwilker · 2022-01-13 18:09

I have a factory installed heater w/ the vacuum controls that is giving me trouble again. Two years ago I replaced both the regulator valve (B7A-18502-A) and the vacuum control valve (B7A-18495-A) and it has worked great until recently. Now it seems some times heat comes out and then suddenly it goes cold again without me touching the heat selector. I tore it all apart again and put a small handheld vacuum pump on the regulator input with a vacuum gauge on the output. Took it up to 15 pounds with the control open and it passed and held the vacuum. Did the same thing with the control closed with the same result, although touching the bimetal strip released the vacuum on the output. Holding the bimetal strip and applying a vacuum on the input did not pass the vacuum to the output, however the input vacuum bled away after a minute (a vacuum leak?).
Then I hooked the vacuum pump to the control valve and while I saw a momentary rise in vacuum, it did not hold the vacuum. I observed the valve inside the housing while doing this and did not see any movement.
So it would seem that at least the control valve is bad. This was a NOS part and maybe the rubber diaphragm failed. Not sure if the regulator if functioning properly. I guess my choice is to replace the control valve and try again or maybe go with one of those mechanical valve kit/adapters. What say you?

lalessi1 · 2022-01-14 08:15

My car was manufactured in May of '57 and it came with the mechanical style of control valve. That is what I prefer. It seems it may be a later running change in design???

thomasso · 2022-01-14 10:53

B7A 18495 A valves are pretty dependable, however all the available ones were probably made in the 50s or 60s so the rubber parts are probably somewhat hardened. So may have a shorter life I have a number of these valves and regardless of the packaging are identical other than Dole brand which are marked. I believe all were mfg. by Dole and supplied to other labels. FOMOCO boxed ones are identical. To my knowledge the mechanical valves were used on box type and dealer installed heaters. I personally would stay original.

lalessi1 · 2022-01-14 11:24

The mechanical valve on my car was factory installed as per the build sheet. Here is a picture of it after was rebuilt by the guy on the business card. Probably very little rubber in it.

jdwilker · 2022-01-14 12:00

thomasso,
I see a number of these on ebay by different manufacturers. Some appear silver and some look like they're cad plated. Would one or the other be a newer build? Trying to find some fresher rubber.

thomasso · 2022-01-14 13:00

Forgot about the thermostatic valves. Don't have my parts book handy. They are much rarer than the vacuum ones. Maybe an assembly plant thing?

hiball3985 · 2022-01-14 15:15

I have the same valve as Lynn. The less vacuum lines the better in my opinion.

KULTULZ · 2022-01-14 16:01

Quote from: lalessi1 on 2022-01-14 11:24

The mechanical valve on my car was factory installed as per the build sheet.

Is there any possibility of your scanning and posting that sheet?

lalessi1 · 2022-01-15 08:39

Here is a pic of my build sheet. It was stapled to the back of the right door panel.

KULTULZ · 2022-01-15 17:26

That is much appreciated!

I have never seen one that early. All I have records of are a few GATE RELEASE forms.

KULTULZ · 2022-01-15 17:48

Quote from: thomasso on 2022-01-14 13:00

Forgot about the thermostatic valves. Don't have my parts book handy. They are much rarer than the vacuum ones. Maybe an assembly plant thing?

Below is MPC TXT for the valve(s) -

The MPC or the SHOP MANUAL does not explain the different usage.

mustang6984 · 2022-01-16 21:11

Is it something you could take apart yourself...and replace the diaphragm? Make one out of a bicycle inner-tube? Just throwing ideas out...

jdwilker · 2022-01-17 10:50

The control valve is pressed together so you can't easily take it apart. I may cut it apart just to see what went wrong.

mustang6984 · 2022-01-17 10:57

Well...it was a thought...phooey.

jdwilker · 2022-01-18 11:23

I cut open my old control valve and this is what I found. The diaphragm is made from a very thin rubber coated mesh. It's a tough material - hard to tear. However, as you might have guessed, the rubber is old and seems dry, almost brittle. I found the perforation that caused my failure near the edge, maybe caused when it was originally assembled. Since the only replacements out there are likely the same age, this could be a chronic problem. I'm ordering another NOS valve that I'll vacuum test first, but if that doesn't work out, I'll be going with that mechanical valve adapter.

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Vacuum heater controls