Automotive Air Conditioning Information Forum

So, I loaned out my beloved gauge set. I know, bad move.

The set was given to me by a friend thirty-five years ago. Probably one of his older sets then. (He was an HVAC technician) When I went to work on my truck today, I noticed that the low pressure gauge is resting at 45 psi when it should read zero. What happened to it? It's easy to suspect that it got over pressurized.

Remove the front cover, may be glass or plastic. Sometimes they unscrew, sometimes they are pry off. Be careful.
Down at the bottom close to Zero you will note a slot head screw. This is a zeroing out adjustment for the Bourdon mechanism inside the gauge. Have at it.
I bet your set has a sight glass built in.

In a worst case scenario i have taken the back off the gauge and tweaked the Bourdon mechanism to reset, but this is seldom needed.

This is why I am loathe to loan my tools, they always come back broken. Now I tell ppl, buy your own then you can break your own

It can only be adjusted down to just below 40psi. I set it at 40 and subtracted that from read pressure. Of course I'll try the pliers.

I was actually just wondering what caused it to tweak so badly.

Replace the gauge if it took a hit that hard. Low side R12 gauges typically have a 100 - 120 psi range and a snubber for those little "accidents".

When you hit one hard enough to bend it to 45psi permanently it may never register accurately again.

Newer 410a HVAC systems can see 350+ psi on the low side static on a warm day. And over 500 easily on the high side. If your friend borrowed it to work on the average mini-split...

FWIW: The gauge is toast. I gave the Bourdon Tube a little nudge where I could dial it in to zero. Opened the can of r134a I had used last and high side went to 75psi, the low side to 100psi.

New gauge is cheap.

Bohica nailed it, your friend used it on his home AC, which is R410, which uses very high pressures, and killed it

Actually, he used it on a thirty-five year old R22 unit on his boat.

That is odd, depending on ambient, he should have been around 50/250. Maybe as high as 60 on the low.
He did something wrong.
Maybe switched the hi and low sides by accident

tbirdtbird wrote: ↑Mon Sep 13, 2021 2:10 pm Maybe switched the hi and low sides by accident

That sounds like it.

Ordered a new gauge. After it comes in, I'll be back for help sorting my truck's AC. Which is cooling great by the way.

akaDigger wrote: ↑Mon Sep 13, 2021 6:55 pm Ordered a new gauge. After it comes in, I'll be back for help sorting my truck's AC. Which is cooling great by the way.

Never trouble trouble until trouble troubles you !!!

What's to sort out on that truck?????????????