Check oil drain solenoid for any debris or damage inside the solenoid flunger. Replace/rebuild as needed. Hope this will solve your problem. Don't forget to vote for my solution
If you have less than 10lbs of refrigerant in the tank and you're changing modes, this can happen. If this is the case, Tech Support can help walk you through a reset process at 800.822.5561
may be the cause is no power source, try to check voltage reading at your breaker, if the breaker itself has a power then the problem cause at your ROBINAIR, if you have guts to open the unit ?, try it and find which cause the trouble , thank you and GOD BLESS.