Pioneer YN018GMFI16M2D Service Manual page 28

8.5.9 Compressor preheating functions
----Preheating permitting condition:
If T4(outdoor ambient temperature)＜3 and newly powered on or if T4＜3 and compressor has stopped
for over 3 hours, the compressor heating cable will work.
----Preheating mode:
A weak current flow through the coil of compressor from the wiring terminal of compressor, then the
compressor is heated without operation.
----Preheating release condition:
If T4＞5 or the compressor starts running, preheating function will stop.
8.5.10 Compressor crankcase heater
When T4<3 and the compressor is not running, the crankcase heater will be active.
When T4≧5 or the compressor starts up, the crankcase heater will stop work.