Originally Posted by SAM@GTM

The reason why I asked you to check the refrigerant high and low pressure is not to find out whether or not you have enough freon, but to really get a good idea of how the system is operating mechanically.

If you go to the doctor and you are feeling dizzy, what is the first thing they check? Your blood pressure!!!!! Checking the refrigerant pressure is the exact same thing. It has nothing to do with how much refrigerant there is. In fact, sometimes, having too much will cause problems. The pressure differential between the high and low sides must be within a certain range. If the pressures are out of spec, then there is a problem. Remember, the pressure is going to be related to the ambient temperature.

Once we are done with AC 101 basic testing, then we can move forward. If your AC high side pressure is higher than normal, then the factory ECU will shut down the system due to excessive pressure to protect the system. If your low side is too low, then the system will also shut off the AC. If your pressures are perfectly normal according to the ambient temperature you are in, then there could be a mechanical issue. Also, if your system has been disconnected for the radiator replacement or a turbo install, and the system was not vacuumed out, then that will kill your AC performance because moisture in the system will cause major problems. That's why you have a receiver dryer to keep the refrigerant free of moisture.