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Schraeder valve leak?

Kestas on Sat August 11, 2012 7:21 PM User is offline

Year: 2001
Make: Mercury
Model: Sable
Engine Size: 3.0
Refrigerant Type: 134a
Country of Origin: United States

The Sable a/c has worked flawlessly since new. Three weeks ago I put gauges on it to verify the gauge function. I did this because I was working on a friend's a/c system. I wasn't sure the gauges were working. I've only used the gauges a handful of times in the past 10 years. Three weeks later, all the refrigerant escaped.

I added one can of refrigerant. Suspecting the ports, I threw some soapy water on them. The low side port immediately foamed. Is it supposed to do that? Or have I found the problem? I'm not sure how much is too much.

Dougflas on Sat August 11, 2012 8:59 PM User is offline

The schraders are common to leak somewhat. The cap is the primary sealing device. Make sure there is a sealing gasket in the cap.

AutoCool on Sun August 12, 2012 5:06 AM User is offline

Any leak big enough to produce soapy foam is a HUGE leak. Have the refrigerant recovered, replace both schrader valves, and vacuum/refill with the proper refrigerant amount. There's always a chance of another leak point, have the system checked with an electronic detector. UV dye added to the system will help pinpoint any future leakage.

The LP port often leaks at the schrader valve because of the lower pressure. The HP port has higher pressure helping to keep the schrader valve shut. I believe Volvo is the only car maker that uses metal caps and double seals on the ports. In extreme cold weather the AC system pressure can enter a vacuum and cause a weak schrader valve to open and draw in air. Even if the AC system is properly charged. I ALWAYS replace schrader valves for that reason. Here's a pic of a (Volvo) schrader valve cut apart, not much there really. The coin is about the size of a USA quarter.





Edited: Sun August 12, 2012 at 5:10 AM by AutoCool

NickD on Sun August 12, 2012 8:22 AM User is offline

We must live on different planets, on my planet, Schrader Valves are history for MVAC applications. R-134a ports use all quick connect couplers, not much different than a quick couple on an air hose that always leaks. Uses a fairly large diameter neoprene disk that never seems to reseat properly causing leaks. Typically not replaceable unless you change the entire line that valve is located in.

Your only line of defense is to replace that now plastic cap and make sure it has a piece of rubber inside. All this was done when the EPA became interested in refrigerant leakage. Letting the manufacturers get away with murder, but creaming the techs if they release the last ounce of refrigerant into the atmosphere. Recover what?

At the same time, GM drops their famous trouble free ceramic seal in favor of a single lip neoprene cell, Ford comes out with springlok couplers, Chrysler with rotten evaporators, Japnese really cheapened up their AC systems with corrosion problems, all this is fine with the EPA. All kind of alternative refrigerants came into play, EPA approved along with death kits. Each requires a unique port because its assumed the tech can't read.

What was never a problem before, is now a major problem, all in the interest so claimed to protect the environment. I give up.

Cussboy on Sun August 12, 2012 10:19 AM User is offline

Well stated, Nick.

AutoCool on Sun August 12, 2012 11:24 AM User is offline

So basically there are no AC schrader valves on a 2001 Mercury Sable? OK, in that case,well stated. Can't argue with a senior member.

Kestas on Sun August 12, 2012 1:54 PM User is offline

The inside of the port looks like a tire valve, like the pictures AutoCool shows. After posting, I kept blipping the valve until it sealed. there must've been some grit there. I blipped it a few more times, and it still seals properly. I checked the static pressure yesterday and today - no change. So I trust it's holding the charge. I finished charging it and checked the LV port (no leaks), so it looks like I'm good. UV dye was added yesterday.

Thanks for the advice of checking the cap seal. I thought it was just a dust cap.

Edited: Sun August 12, 2012 at 5:29 PM by Kestas

NickD on Sun August 12, 2012 2:03 PM User is offline

You can lose over 97% of your refrigerant without seeing any change in static pressure. What really changes static pressure is the ambient temperature. A 20*F change in ambient temperature can change your static pressure by around 25psi. If you check it at -35*F, would be 0 psi, even if fully charged.

Leggie on Sun August 19, 2012 12:02 AM User is offline

Quote
Originally posted by: AutoCool


The LP port often leaks at the schrader valve because of the lower pressure. The HP port has higher pressure helping to keep the schrader valve shut. I

Do you have anything that supports this claim? Both ports spend most of the time with exact same pressure behind them. There's only a pressure difference when the A/C is operating and several minutes thereafter. They're held at the temperature of refrigerant pool within the car all other time.

buickwagon on Sun August 19, 2012 2:48 AM User is offline

I've seen a number of Fords with Schrader valves -- larger diameter than the type used in tires, but a Schrader design nonetheless. I have a box of new ones and now change them regularly since older ones have a tendency to start leaking once disturbed. I also have a selection of the "rubber flap" style R-134a connectors. Popular on many GMs, the seal itself is not replaceable, but the complete port threads into the line and is easily replaceable (an 8-sided socket is required) without having to replace the entire line. Oddly enough, I have found the high-side more prone to leakage with that design.

Just my 2¢. Your mileage may vary.

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I've saved hundreds on service by spending thousands on tools.

Leggie on Mon August 20, 2012 3:27 AM User is offline

All being equal, my guess is that low side is more likely to leak form usage. DIYers typically leave the high port alone like a plague, but low port is where people hook up their can-o-gas

Toenail on Wed August 22, 2012 5:35 PM User is offline

I don't know about Fords and their Schrader valves but I know my Tahoe has one on the low pressure side and a ball valve on the highside port. Both leak from time to time. I found the cure with some nice brass plugs that have an O-ring built into them. Threw the plastic caps away and no more problems. Saved a bunch compared to the replacement cost of the port valves. The valves cannot leak with the plugs installed.

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Toenail

Leggie on Wed August 22, 2012 9:58 PM User is offline

Quote
Originally posted by: Toenail
I don't know about Fords and their Schrader valves but I know my Tahoe has one on the low pressure side and a ball valve on the highside port. Both leak from time to time. I found the cure with some nice brass plugs that have an O-ring built into them. Threw the plastic caps away and no more problems. Saved a bunch compared to the replacement cost of the port valves. The valves cannot leak with the plugs installed.

You may have galvanic corrosion. When it gets wet and there's a trace of road salt the, the brass cap becomes the cathode and aluminum port becomes the sacrificial anode. So the corrosion will take place on vehicle line side.

This is not an issue with residential A/C system, because both the port and cap are valve, therefore no galvanic action takes place.

Just use a valve core tool that lets you hot swap the core without pulling the charge.

AutoCool on Thu August 23, 2012 5:31 AM User is offline

Quote
Originally posted by: Toenail
I don't know about Fords and their Schrader valves but I know my Tahoe has one on the low pressure side and a ball valve on the highside port. Both leak from time to time. I found the cure with some nice brass plugs that have an O-ring built into them. Threw the plastic caps away and no more problems. Saved a bunch compared to the replacement cost of the port valves. The valves cannot leak with the plugs installed.

Good thinking!

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