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i'm trying to charge my A/C, and i've been looking up instructions and numbers to judge as correct pressure amounts.
all the pressure amounts i've read say "low side pressure". is that with the compressor on, or without?

Low side pressure is the low pressure side regardless of whether the compressor is on or off. One set of hoses is high pressure the other is low. It is on the low side that you will be adding refrigerant to...while the car is turned off...but I cannot tell you which side is which.

yeah, i know all that...i was watching the pressure while the compressor was turning, and it was normal, and when i turned it off, it shot way up, and i wasn't sure if it was supposed to happen like that. i guess i'll go check it again now that it's been sitting

Turn ON the engine and START the AC (on max). You hook up to the low side, then let the refrigerant flow. The low side is actually like a vacuum and will allow the refrigerant to go in.

yeah, i did that already. what i meant was, while adding refigerant to the running system, the pressure gauge said the system was at about 35 PSI, and i stopped filling it. then i turned off the car (and the A/C too) and the gauge went up to about 70 PSI. so i freaked out thinking i added too much refrigerant. funny thing: nobody's really told me yet whether i have or haven't, and none of the instructions for the charge kit makes this clear. or maybe it has been totally obvious and i'm an idiot.

nicklikesmilk wrote:yeah, i did that already. what i meant was, while adding refigerant to the running system, the pressure gauge said the system was at about 35 PSI, and i stopped filling it. then i turned off the car (and the A/C too) and the gauge went up to about 70 PSI. so i freaked out thinking i added too much refrigerant. funny thing: nobody's really told me yet whether i have or haven't, and none of the instructions for the charge kit makes this clear. or maybe it has been totally obvious and i'm an idiot.

The pressure when the system is turned off equalizes throughout the entire system. It's a function of charge and temperature around the various components at that time. For what you're doing it doesn't mean anything related to the amount of charge. It's what the pressure on the low side of the system is with the motor running and the AC on high ends up at. Yours is at 35 psi and I believe up to 45 is indicated for the R134a charging can/kit gauge from id at Walmart as normal--maybe it's even 50.

ahh, that is much helpfuler (i know that's not a word, but i had to use it anyway).

so then, that pressure spike when it's not running is normal?

Yeah it is normal and if you had the refrigerant can still hooked up your lucky it didn't blow your head-off. Leave the can hooked-up (withe the AC on max) the can will get cold (vacuum effect). When the can is no longer cold, your done. Un hook the hose, from the car side first, then dispose of the can.