What is the correct pressure on the high side and the low side of an efficiently working system?

Answer 1

High side <200psi. Low side <50 lb.
"A good rule of thumb with R134a is to run fan on High with all windows open and engine at 1500 rpm. High side pressure in PSI should be about 2.2 to 2.5 times outside air temperature in degrees F"

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There are NO easy answers to this. Most manufacturers provide a chart or charts that will assist in determining what those pressures will be. The variables that will affect those pressures include, but are not limited to: Outdoor ambient temperature Outdoor relative humidity Indoor entering temperature (wet bulb or dry, depending on rel. humidity) Unit and duct sizing and proper airflow through system Some techs will use "rules of thumb" and dead reckoning that may have worked in the good old days, but with ever rising costs, newer systems are more demanding and a simple refrigerant miscalculation could cause performance problems resulting in comfort concerns or higher power bills. If this is true, then why do the gauges you use have a chart on them that tells what the high side range and low side range should be? Also, if this is such a cryptic answer, then why can I buy these gauges at a tool store for about $20? The low side should be anywhere from 65-80 psi (40 degree coil temp) The high side should correlate with the outside temp... The gauges have pressure temp for each type of freon being used,for example using R-22 freon on a outside ac unit,40 degrees will equal to 70 psi on the gauges (suction/low side) gauge Sure, you can buy guages at a tool store. I fix a lot of repairs made by do it yourselfers. The chart on the guages are for corresponding pressure to temperature, not to tell you how much gas to put in. The best, most comprehensive measurement is superheat: suction pressure converted to temperature and a measurement of suction line temperature. this tells you how the refrigerant is acting in regards to the total (sensible and latent) amount of heat it is removing from the air.