1990 GMC Truck Pressure and Temp Recommendations

I don't know of a set pressure that they should be at, but this is what I remember on the subject
they should be within 10 PSI from each other with engine off, using high and low pressure gauge to check
the compressor should cycle on at (41-51 PSI)and cycle off at (20-28 psi) so if your system is running with pressure (20-28 PSI )you are low and need to add and check

or maybe you are looking for this www.

Chillers. Com/PT%20charts%20for%20refrigerants. Htm

Hi gphillips123, Welcome to 2carpros and TY forthe donation

I used this as a guide-see below

LOW pressure gauge: Normal when its between 25-40 psi

High pressure gauge: Normal at 200 to 225

Note: Anything over will cause the system toovercharge

I don't have the temperature readings-Sorry