Decelerator or Hand Throttle (STD cab) Position potentiometer voltage is too low
High range clutch is not calibrated
Aux 3rd Lower solenoid failed open or short circuit.
Low pressure switch (-) input shorted to power
Foot Throttle Position potentiometer voltage is too low (engine controller pin B30)
High range clutch is not calibrated
Partial frosting and sweating of lines combined with poor cooling, fan belt slipping, loss of refrigerant, restricted or clogged liquid line or expansion valve malfunctioning.