5 Simple Service Valve Tips

Service valves are so basic, and we see them with such regularity that we can miss them altogether.

Before I give the tips, I want to address the tech who tells the customer it was “probably the service valve” or “the caps were loose” as a plausible reason for a leak without actually making a proper diagnosis. Don't make excuses; find the leak.

Now, let's go over some tips.

#1 – Look before you connect

Look for oil around ports BEFORE you connect your gauges every time. If you have a leaking Schrader and cap, you want to know that before connecting your gauges and eliminating that leak. Keep in mind that a service cap is NEVER meant to be the seal from a leak; it does act as an insurance policy against a tiny leak in a Schrader. If you find a leaking Schrader, replace it.

#2 – Be gentle with the heat 

No matter the valve, make sure you protect it from heat when brazing or soldering. (I'm looking at you, Staybrite #8 techs.)

The Schraders should be out when brazing anyway, but the internals of the valve are also sensitive to heat. Ever see a valve leaking from the stem? Odds are, it was overheated at some point.

When opening and closing the valve, DON'T CRANK DOWN so hard. We all know you are strong, but when you crank it open and closed like that, you can over-compress and damage the seals and mating surfaces. Snug is good, but if you need to “put your back into it,” it's probably too much.

#3 – Check your seals

A 1/4″ service port is actually just a 1/4″ flare fitting. Technically, they don't NEED a seal if the cap is a flare cap (think Trane brass caps). The only trouble with the brass flare caps is they DO need to be on pretty snugly to seal.

Most manufacturers have gone to caps with a rubber O-ring seal inside. These caps seal better, and they only need to be finger-tight. Before installing these caps, get in the habit of checking the seal EVERY TIME. Make sure it's there and that it's flat.

I've seen many leaks caused by an O-ring that got put in cockeyed and depressed the Schrader slightly when the cap was installed.

#4 – Try the newfangled technology

We always used to advise using a bit of refrigerant oil when making flares and even when reinstalling the top caps on service valves. The oil doesn't really “seal” anything, but it helps you get a snug fit without twisting or damaging anything (the technical term is “galling”).

The trouble is, we are going away from mineral oil and toward POE, and POE fouls if it is exposed to the air (humidity) for too long. Granted, a drop of mineral oil on a flare isn't going to hurt a POE system, but IT'S THE PRINCIPLE, DANGIT!

I have raged against the use of thread sealants like Leak Lock in refrigerant circuits for years. I've seen Teflon tape and Leak Lock on flare fittings and Chatleff fittings. Teflon tape and Leak Lock do not belong on refrigerant circuit components, folks. They aren't designed for that purpose, and if they get into the system, they are gonna cause issues. In many cases, gumming up the threads and mating surfaces with these products can inhibit a good seal by getting between the flare mating surfaces.

A product I like is called Nylog. It's a very thick but constantly viscous product (never gets hard), and it won't hurt the system if a little gets inside because it's made of refrigerant oil.

You can put a drop on the threads and mating surfaces of all your flares, chatleff connections (the valve connections with the Teflon seals), top caps on your service valves, pipe threaded ports, everywhere—but just a drop.

You can also use it on your hose connections to get a better seal when pulling a vacuum.

Just use a small amount. Otherwise, dirt will stick all over everything.

#5 – Using the right wrench and back it  up 

For those systems that still use flare hex caps, it's best to use a 9/16″ box end wrench or flare wrench (shown above) and use a backing wrench when removing the cap. All it takes is ONE TIME of breaking it off to regret using a big ol' adjustable wrench.


P.S. – If you'd like to learn about multi-position service valves, particularly in refrigeration, you may want to read this article we wrote.


Barry Allison
Barry Allison
2/5/17 at 03:59 PM

Totally agree ,except for one point . Teflon tape on the thread of the suction side of the TX valve . Your thoughts ? Thanks mate . Barry .

Yilliang Peng
Yilliang Peng
4/12/17 at 12:41 PM

Thanks for the advice to look for any kind of oil ports before you connect the gauges. I have been trying to figure out this valve at home for a couple hours now and was unaware of that. With that being said, I think that this information would be perfect for anyone who is working in the industrial field. Thanks again!

9/3/19 at 07:19 PM

“Most manufacturers have gone to caps with a rubber O-ring seal inside, they seal more EA skirt and they only need to be finger tight.”

What is an “EA skirt”?

Jason Hewett
Jason Hewett
9/4/19 at 03:33 PM

When you purchase a Sporlan replaceable core Filter Drier, they provide you a 1/4″ plug that can be installed in the shell lid if you do not prefer to install a 1/4″ Service Port. The Sporlan supplied plug comes in a bag that states… Only use Teflon Tape on plug threads.

6/27/21 at 09:01 PM

What type of elastomer seals are acceptable? Not just any type of elastomer seal (o-ring, schrader, etc.) is acceptable for exposure to some types of refrigerants?


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