When this error is thrown, the pressure gauge on the side of the unit will often be very low, or even at 0. 

(This gauge reads normal while the heat pump is at rest)

Refrigerant Leak: If the pressure gauge reads 0 or if you have exhausted all other troubleshooting, remove the side panel off the Arctic Heat Pump and check for any signs of a refrigerant leak. Refrigerant is an oily substance and will usually pool at the bottom of the unit. You may have to check under the compressor and/or heat exchanger.

If a refrigerant leak is confirmed, have the leak fixed, vacuumize the system and fill with refrigerant according to the information on the technical label.

NOTE: It is also common for condensation to form inside the unit. If you find liquid and it is not "oily", it is likely condensation which is nothing to worry about.