"sticky" shraeder valves at hi/lo port

[r-mm]

I replaced the valve cores in my R134a adapters using these parts https://www.amazon.com/gp/product/B075W ... UTF8&psc=1

I've used those same cores on other projects with success. Today I pulled the manifold quick connects off the high side with the engine off (I was reading static pressure) and heard a slow low hiss. It was not just a squirt of pressure it was a long slow hiss. I reseated the quick connect a few times, operating its handle and got the hiss to stop. Has anyone seen this? Is it likely a valve core issue? Where would you buy the best primo A++ valve cores?

[r-mm]

Thanks for responding, its good to know someone had a similar problem. It also occured to me that the low side experiences suction which acts against the valve. I realize most small parts like this are made in china these days, maybe by one company. What would "pros" use? Are there different types of seals etc?

[JohnHere]

A few comments: With a properly operating system, the low side shouldn't show negative pressure (In. Hg.) on the manifold gauge set unless there's a blockage of some sort or a problem with the metering device (TXV or OT). The Schrader valve on the low side should be seeing positive pressure of around 30 PSI under typical operating conditions. Also, after replacing the cores, be sure to install port caps (preferably new ones) on both the low and high sides because the caps do the final sealing.

As for the Schraders themselves, I've used valve cores from FJC, and I've never had any problems with them leaking as you described. You'll find one variant here: https://www.centurytool.net/Jra_Valve_C ... jc2674.htm
(Please note that I am not affiliated in any way with FJC or Century Tool.)

This site's sponsor, ACKits.net, offers high-quality professional-grade parts as well.

[JohnHere]

I think I'm responding to r-mm and not Al9. But sure, go ahead and lubricate the entire valve core with mineral oil (compatible with R-12) or DEC PAG (compatible with R-134a) just before installation. Doing so will help the o-ring and the valve itself give the best possible seal.