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A/c recharging

I hooked up the pressure gauge to my car today to check psi in the system prior to recharging and got 0 PSI (refrigerant disconnected), which seems impossible because the compressor was engaged and the a/c was cooling to around 60 degrees.

Does my can of refrigerant need to be at the other end of the hose for pressure to register ? I don’t want to risk recharging w/ a bad gauge in order to not overcharge the system. Advice ? Thanks.


Update: I tried checking the pressure with the can connected at the other end (was careful to not puncture the can) and still got 0 PSI. Do I have a bad gauge or is 0 PSI correct and I should just go ahead and charge until the pressure is within the proper cooling range ?

Zero is not correct.

I concur. Bad gauge.

Question, Are you sure you are not connected to the vacuum side?

It’s also likely that the pin in the gauge connector is not depressing the valve in the car’s service fitting for some reason.

what are we working with? (FGS),year ,make ect.)R12,134-A. full gauge set (wal mart stuff)need more info?

and when in doubt charge by temperature.

you say 60 degrees ,I respond what was the ambient temp?

dual A/C? single unit?

The suction side is the charging side. The pressure should still be 25-45 psi. Any lower, and the low pressure sensor will turn off the compressor. The one in my car trips at 18 psi. The high side uses a much larger port, and can get to 250-375 psi. You cannot fit a charging port to the high side by accident with an R-134A system.

87 Accord, 134a, partial gauge set (low side only)

Ambient temp was approx 70 degrees.

Single A/c

Should I throw out that gauge and try another ?

so i assume it has been converted to 134-A ?


Hopefully, no one bypassed the low pressure cutoff switch.

Make sure the new service port is full screwed down onto the old valve. I suspect ok4450 is correct that the valve pin isn’t being fully depressed.

is that the same gauge that came with the can of 134a? because their not accurate at all.they sell better gauges seperate from the can.that is what i had to do.