CarTalk.com Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show

AC Pressure Problem

I am working on charging my AC system and I am running into a problem with pressure readings. This is an R12 system with R12 to R134a adapters.

I have two manifold gauge sets, OR and AZ. If I connect OR I get a hi side pressure of 50 PSI. If I connect AZ I get a hi side pressure of 5 PSI. This is reproducible - I can move back and forth and get the same readings.

I moved the red port connector from the OR set to the AZ set. Now the AZ set reads a hi side pressure of 50 PSI.

So the OR red port connector gives 50 PSI and the AZ red port connector gives 5 PSI, regardless of the hose or gauge it is connected to.

The OR set is used and the AZ set is brand new.

Both port connectors have about three turns from fully open to fully closed. When connected to the car both connectors can be turned about 1.5 turns before they stop.

What could be going on here?

Thanks!