Greetings,
>
> I have a 1998 C-1500 with a 350. It has about 50,000 miles on it, and
> currently is driven about 4000 miles/year. I've been having problems with
> the AC where sometimes it works, sometimes it doesn't work. Even when it
> doesn't work, the clutch on the compressor is kicked in (ie the compressor
> is on). If I turn it off for a while (10 minutes), and turn it back on it
> works again.
>
> I went out and bought a R-134 pressure gauge, and attached it to the low
> side, and it was registering 37 PSI with the AC temp set to max, and the
> fan on high. The outside temp was about 85 degrees.
>
> According to the instuctions with the gauge, the pressure is supposed to be
> 45-55 psi at that temperature. Is this true for all R-134 systems, or does
> this vary by vehicle? If it does vary, is there an outside temperature to
> low side pressure table available anywhere that I could see?
you see, this is how it is:
the low side pressure is directly related to the evaporator temperature (don't know if your gauge has both pressure and temp scales on it)
the lower the pressure, the lower the temperature
below about 40 degrees in a 134a system, the temperatures are below 32 degrees
thus, the evaporator will freeze the moisture in the air passing over it, and ice up solid
in an R-12 system, the old 'rule of thumb' was a degree per psi..........keep presusre above 35 or so, and you were OK
R-134a takes a bit higher pressure to keep you out of the frost zone, tho
hope this helps