Bad gauge

[Tommer2]

trying to vaccum my system. Hooked up the gauges turned pump on. Low side not sucking high side is. Unscrewed low side hose from gauge I feel it sucking. Since I saw the high side sucking a little I switched gauges to see if the low side gauge would suck a little on the high side line it didn’t. The high side gauge I put on the low side did draw down a little. Do I have a bad low side gauge? Thanks guys.

[Cornbinder89]

Sound like it.

[Tom Greenleaf]

I'll try to be concise about gauges: First there are different types to you need to know you exact gauges. You should be able to vacuum out just the hose from a pump (Yellow hose) to manifold/gauge set, with blue hose plugged should read in seconds the full vacuum on blue gauge and again do read hose. Can be argued it you need to vacuum both side? NO. It's one system and almost can't plug so tight that entire system doesn't get the full vacuum.

Common to maybe just me. Hoses frequently have two ends, one end is required to depress a Schrader valve or nothing is going to happen there it can be right and valve or gauge hose end screwed up? If it's working you can see the red gauge also show the same vacuum if good gauges but then close that not really needed again if it holds is the other issue. Where isn't it holding if it doesn't? Bad hose, manifold set or connection at the car's end? Hard to know for sure it can be the vehicle not the gauges, bad ports cheap gauges or you left red side open!

What condition is the pump's fitting? All these hoses use a rubber seal and any can fail - worse new doesn't always solve it.

Gauges also either have places to "Park" hoses when not in use. Some seal there some are just a spot to get them out of your way you need to know.

Gauge hose ends may have screw or ball valve shut offs at the ends and or screw on to fittings or pull back like you do for common air tools.

Yup - gotta know your gauges are good and can compare accuracy with another even better.

In your head you must think and know where is known full vacuum or just atmospheric pressure no good don't allow even that in when charging time comes!

Learn your gauges and where they can fail before even starting or the info can't be trusted just wasting time. Just me - can't live without two sets of known working gauges when anything isn't right try the other and all that just to make a known full vacuum and know it's real and then that it holds!

Don't lose all your hair if you have any but this first then proceed. If needed can make up hose end plugs out of retrofit fittings and a union and have done so myself what everyone else does I can't know of course but I do know where what is and where to look for the problem with they do not cooperate you do too,