A/C high side gauge "stuck?"

[D60]

I just attempted a/c service for the first time. Vehicle is '15 Forester.

I had a new Mastercool manifold gauge set. After charging the high side would just creep more and more....for awhile hanging around 400, then 425, then 475 and finally settled around 500 which is the max but I see no peg to stop it from going further.

During this low side was around 40 at 75* ambient and a/c was blowing cold.

It didn't make a lot of sense (plus I'm not sure the system could withstand 500psi) so I finally decided to just try removing the high side line and re-fitting it.

Suddenly I was back to pressures in the 200's which seemed far more reasonable.

It is possible I had the low loss valve screwed in too far because the system came to me with no charge, so it was difficult to know when it had depressed the Schraeder enough. Maybe this created a "check valve" situation??

Has anyone experienced anything similar?

Also the Mastercool can tap I got likes to leak. Sometimes a little, sometimes a lot. Seems the needle valve doesn't seal well.

I'm wondering if Mastercool isn't as good as I hoped? Or is this all user error? I'm inclined to send both the manifold gauges and the can tap back, but maybe I just need to get more smarterer??

 

[D60]

Well I called Mastercool tech support 888-825-6989 and spoke to a guy who wasn't incredibly helpful. He said sometimes my condition can occur if you start the vehicle with the "front" valve opened. I asked if the front valve was one the one on the manifold and he said yes.

Didn't make a lot of sense to me -- not sure why you'd have that valve opened when starting. You don't charge the high side so you don't need to join it to your yellow line and if you left it open you'd just evacuate the system. He also couldn't really tell me if the gauge was damaged from going to 500psi but acted like it was a definite possibility. Overall he didn't seem concerned and just wanted to get me off the phone.

My main issue is just trusting that gauge in the future. I paid a bit more for Mastercool hoping for greater durability and accuracy than, say, Harbor Freight, but now I'm not sure I trust the high side readings next time. I'll likely return the whole kit to Amazon while I'm within the return window.

I'm looking at perhaps the Robinair 48510 but it looks like their low loss fittings don't have a needle on a knob you screw in after clipping them on. I wonder if this is really a concern in actual use?

 

[JHZR2]

It would seem to me like a needle that is not set correctly or perhaps slipping on its shaft. I don’t see how you would get to such pressures even during some transient spike without other issues.

 

[D60]

Yeah, I dunno and sadly I'm not qualified to make conclusive judgments....but I no longer trust it.

I started an Amazon return and ordered the Robinair....best price was Zoro and a 10% code made it even better. Still around $200 (with tax)