i was curious to know more about the pt chart, i feel like im missing some thing i see alot of people ask what should be the correct operating pressures for X refrigerant. the way i determine the pressures for example r22 cooler with a low pressure control as a temp control. cut in is about 72 psig = 42 degrees then to determine the cut out temp would be your desired box temp ex: 35 degrees = 61 psig then minus the 15 degrees td would be 45 psig cut out = 21 degrees evap coil. (this will get you close, but many variables will affect the cut out/ cut in pressures.
if i work on something im not familiar with, the best is to call tech support and ask the operating pressures. if you can thats always nice. but sometimes they never return your call. so basically ill go off the box temp minus 15 delta t will get me close then check my superheat and comp. amperage.
but some evap coils are designed with 10 degrees td. Can you give me more pointers or more ways i can use the pt chart as far as figuring pressures.