Automotive Air Conditioning Information Forum

Can someone explain why low side/high side gauge pressure charts vary so much? For example I see charts that show, at 90 degrees, a low side of approx. 30 psi and high side of 225. Another chart will show 50 PSI and 260 PSI? One chart even allows for differences in humidity.

I know engine RPM, airflow, spraying the condenser with water all have an effect on pressures. Bottom line I never know quite what to expect when I hook up a set of gauges to do a test or charge a system.

Thanks!

Most of those charts are vehicle specific, as published in the FSM for the vehicle. Over the years, people have copied those carts and presented them as universal.

With systems varying wildly, from CCOT to TXV, POA valves, Variable displacement compressors, etc. there is no one set answer. Add in climate, airflow and age?

A FSM for your car may not be very specific, or it may have every detail. All depends on the manufacturer.