My 1995 Subaru seems to only be pushing cold air when the engine is going well above idle. Can someone explain to me what limiting aspect the system would have to not run the compressor unless the car is under load? I did ensure that the system is well charged and when under load (>30mph) I do get cold air.

Sounds pretty typical for an undercharged system. You should probably have that checked again.

It's probably not the load, it's the rpm. Low on refrigerant.

Charge is too low, or the radiator fans are not running when the AC is on.

 

More than likely it's because the charge is low.

Check refrigerant charge and it also often helps to pull a spacer washer out of the compressor clutch to account for wear.

 

GD