Our AC has had several problems and here is what we have learned from the symptoms

PROBLEM	CAUSE
AC relays toggle on & off even with the AC off	The Trinary switch is defective and making the ECU turn on & off the AC blower relay.
System blows hot air (no cold)	Low in refrigerant evaporator inside cab passenger side bad.  condenser (mounted in front of the radiator) has obstruction. Even though air can be blown trough with a air hose it does not mean it is not clogged.
Condenser fan will not come on	Condenser fan relay bad ECU defective since it controls the coil side of the condenser fan relay.