Before you plug it in:
With an ohmmeter, check and see if you have a reading across the prongs on the relay where you attach the cord. If you have a reading, then the heater is good, if not, it's shot.
The heater is most important in a room that is cool.
I'd go ahead and try and run it. It may run fine and not cool. If so, that might be due to non-condensable gases. It may run awhile and trip the relay. That may also be non-condensable gases. It may not run at all, which means the compressor is stalled if it hums or a bad relay or wire if it does nothing at all.
Let us know what it does.