I am a student tech at my factory. I was trying to determine if a roof top condensor AC unit was low on a charge. (r22) I had my gauges attached and used my temp/pressure chart (outdoor ambient temp + 35degrees heat of comp.) and looked up the high side pressure. The actual high side pressure was fluctuating with the condensor fan operation rather frequently. Can you reference the high side for this situation or do you just rely on low side pressures? When calculating what the low side should be (for an AC unit in an office)what temperature do you use? I have been using 45 degrees (minus an addition 15 degrees for internal refridgerant temp) If I use 45 degrees and the air blowing into the cooled room is 55 degrees, does this mean there is a problem? I guess I just need some real world rules vs book theories. Thanks again for your time.