Called out on this unit about a month and a half ago and found it low on charge. Searched for a leak and nothing found. Average outdoor temp about 15 degrees at the time. Unit is remote air cooled condensor one fan. System has a headmaster and hot gas bypass. Added gas to system and it came around, checked over and found fan cycling on cond fan. called local rep and they said it should have a P66 speed contoller. Went back and installed P66 a couple of weeks ago. Called out today that unit is down. About 40 degrees out. Person on site said the fault was internal overload. They claimed to have reset it and it ran for a few minutes. I went to start unit up and found high pressure switch on discharge line tripped. I reset and unit ran. Pressures low and unit bypassing hot gas, LL sight glass empty and receiver glass empty. Added about 6lbs of 22 and things came around. Watched for about 45 min and all seems well. I am not sure if I am truly low on charge or if the headmaster had stuck. Going back tomorrow to check for a leak. Just seems very strange that hp switch was tripped. Any ideas??