I have no knowledge of the ac system in the 540G or any other skidder. But I have fixed a few too many car ac systems. If the pressure is good then the next thing to check is the clutch. Is it engaging or not. Sometimes the clutch will freeze up in the off position (not used during the winter time). Other times, the clutch material becomes thinner making it unable to get good contact. On some cars, it's just a matter of either taking it apart to free it up or removing spacers to get the clutch to move in closer.
If freon was charged on top of air in the system that would cause high side pressure to spike. There is a high pressure switch that should kill the clutch before the relief valve opens. A set of gauges is necessary to diagnose. If you have gauges share the readings.
X2 what Kiko said. You need a set of gauges to properly diagnose and charge an AC system.
The only problem I have with skidder AC, is that i dont have any.... joking, hope you get it figured out