If it ain't broke...
Anyhow, the seal for the fitting lives in the cap. As far as I know, there's nothing in the A/C that would damage the valve core, and nothing in the core that would damage the A/C. If it worked well enough to allow charging the system, I'd not worry about it.
I do know that GM high and low service valve cores are not interchangeable.

<<Anyhow, the seal for the fitting lives in the cap>

I disagree . the seal is definately in the base of the valve stem by design. The cap is a dirt seal for the valve stem, but it does serve as a back up for the stem if it has a bubber washer/ring.
I would also doubt very much that the type of compounds used on a/c systems valves would not be much more stringent than that of a simple tire valve expose to air, if for no other reason than breakdown from refrigerant oils...

I admit it's not a MB service bulletin, but I'd ask if you ever replace the service fitting caps when you find a cap seal missing.

Bulletin No. T-91-66
File in Group 1
Number 74
Corp. Ref. No 971202R
Date March, 1991

SUBJECT: A/C REFRIGERANT LOSS DUE TO LOOSE OR MISSING ACCESS FITTING CAPS

MODELS AFFECTED: 1985-1991 DE VILLES AND FLEETWOODS 1982-1991 RWD DE VILLES AND BROUGHAMS 1986-1991 ELDORADOS AND SEVILLES 1982-1988 CIMARRONS 1987-1991 ALLANTES


This bulletin is being revised to include 1991 model years and to update a discontinued part number for high side valve cap and seal.

1985-1991 DeVilles and Fleetwoods, 1982-1991 RWD DeVilles and Broughams, 1986-1991 Eldorados and Sevilles, 1982-1988 Cimarrons, and 1987-1991 Allantes air conditioning High Side and Low Side access fittings are supplied with a BLACK PLASTIC CAP AND SEAL ASSEMBLY WHICH PROVIDES THE PRIMARY REFRIGERANT SEAL for the service fittings.

Figure 1 - Refrigerant Access Fitting

http://img165.imageshack.us/img165/1319/ac2se.gif

If the cap and seal assembly is missing or loose, a significant amount of refrigerant may leak through the valve core located in the access fitting which could result in poor A/C performance or failure. WHEN SERVICING ANY VEHICLE'S A/C SYSTEM, MAKE SURE ALL ACCESS FITTING CAP SEALS ARE IN PLACE AND TIGHT. Refer to Figure 1. Caps should be threaded on until contact with the O-ring seal is made and then tightened another 1/4-1/2 turn to ensure proper sealing.

High Side Low Side
Valve-Cap and Seal (3/8 x 24) Valve-Cap and Seal (7/16 x 20)
P/N 52451233 P/N 6551640
Parts are currently available from GMSPO.

<< but I'd ask if you ever replace the service fitting caps when you find a cap seal missing.
>>

Sure do, ..it is common pactice..
.. cuz we all know that as the schraders get old , they can leak.
But the point is the cap is not the seal.. it is the cap and in being so, it is a secondary safety dirt cover and back up seal.
that's all.
Like your tire seal, .. same deal... the caps main funtion is dirt, but can also seal a leaking valve.

I guess if we were to refer to the cap as a 'Backup Seal" , we would be in
agreement.
The TSB you use only tells me they had a bunch of poor quality Schraders
on those specific models and that the cap would keep the problem in check without having to go the harder route..

A) Tire valve caps don't (usually, at least) incorporate rubber seals. Nor do they see the pressure and temperature ranges that A/C service fittings do.
B) It's not just Cadillac. I've seen the same thing on many different brands.
C) You can seal a fitting with just a cap and rubber seal (This is, essentially, the way most temperature and pressure sensors seal). Can the same be said of a valve core and no cap?

I'll agree that it's not worth arguing over, and that valve and cap seal are the proper way to insure service fittings won't leak.

Naw. Those model years were the ones still under warrenty at the time of the publication of the bulletin. I've never checked earlier or later, though.

<<Naw. Those model years were the ones still under warrenty at the time of the publication of the bulletin. I've never checked earlier or later, though.>>

The reason for the TSB was cuz the Caddy schraders are not removable/sevicable... note they are high side and factory pressed into the line , so the fixture TSB was the fix and now becomes the seal.

..and , yes we do agree , both make for a safer seal than one ... and I personally will continue to replace leaking schraders with quality refrigeration spec.replacements and leave the others in my bicycle tubes... with the caps on.

GM is a whole different beast with their own style.

When you go to any auto store and see the fittings to convert old a/c systems there are two kinds.

"GM" and "Non-GM"

If they rely on the cap to do the sealing of a leak from the valve...thats just odd. All the cap will seal is a very minute leak from the valve. if there's any kind of pressure, it will leak anyways.

I'm not sure why this isn't obvious....

But there is a $35 tool which allows replacement of the shradervalve with the refregerant charge. It's the BEST way to do it.. I purchased mine from an applicance parts place a few years ago. Took them 2 days to get one for R-12.


Michael

That's because GM used different-sized service fittings for the high and low sides of the system. Most others used the same size fittings and depended on you to know which was which.
I assure you this is not so. If you have access to a leak detector, you can prove it to yourself. Sniff around the cap, then remove the cap and check again.

Arthur:

Again, thanks for the tip about the 7/16-20 hex die.

I was able to smooth out the thread pattern enough to get a good connection with the low side hose.

A/C is charged and blowing 40F air at the vents and not freezing up.

Very good .. long Summer ahead..

Don't forget to put that secondary seal with an O ring on there in case the primary valve stem seal should ever develop a small leak.. :)

Agree with MoneypitSEL. Do a leak test on the valve without the cover and with it, and you'll get your result. They need the cover most of the time. I will confess a lot of my experience is with GM, so maybe it's their problem more than other manufacturers.

I guess GM made the two valve stems different sizes so their service techs at dealerships could tell the difference... Could have just painted them pink and blue...

DS
87 300D
Northern Iowa

<<I guess GM made the two valve stems different sizes so their service techs at dealerships could tell the difference... Could have just painted them pink and blue...
>>

Wrong ..

They made them a different size cuz Idiots could go just about anywhere and get a charging kit /hose with a 7/16x20 fitting on it for $10 and they would try to charge the system from the HIGH side..A Big No..NO.!!!
That is the reson for a different size high side fitting.. .. not for Refrigeration Techs , but to make charging DIY IDIOT PROOF..

I have a problem with my converted 300TE.

I had to get a new fitting for the high side conversion so I could hook up a high side guage.

I finally got a "real" Interdynamics guage set.

Anyway, I was charging my R134 last night. When I removed the low side hose from the fitting I heard hissing!

I put a quick disconnect fitting back on in order to try to keep the R134 from leaking out, but I know I'm close to empty.

If I get the old conversion fitting off, I'm thinking if I can screw another fitting onto my low side port, I might be able to recharge the system before too much moisture gets into the system.

I don't see any valve at all on the low side fitting... I'm wondering what happened to it?

Hoping I didn't mess something up....