Quote Originally Posted by frank View Post
An LP fault usually causes a trip. An undercharge or loss of gas usually causes frosting of the evap.
In addition to low charge, you have to first look air air flow over the evaporator. Low air flow, due to plugged filter, dirty coil or fan not operating at speed, will all show a low suction pressure and possibly a frosted coil.

Try to charge a system with a dirty coil and see what you get...

Ken