Crankcase Heater
Why must the heater be on 12+ hours before startup?
To allow oil break-in and ensure non-diluted oil covers all load-bearing surfaces, reducing friction during the critical initial startup period.
Is the heater controlled by the microprocessor?
No; it is interlocked into the compressor motor contactor and operates independently of the microprocessor.
When is a crankcase heater required?
Required when system charge exceeds values in the Multiples Availability Chart, regardless of system type or configuration.
A crankcase heater is a low-wattage electrical resistance heating element installed on the bottom of an HVAC/refrigeration compressor. It maintains crankcase oil temperature above refrigerant saturation temperature during off-cycles, preventing refrigerant migration and oil dilution. This ensures proper lubrication and prevents flooded starts.
In shop floor maintenance, crankcase heaters are interlocked with the compressor contactor and remain ON whenever the compressor is not running, even when the unit is off. They keep the oil approximately 30–35°C (86–95°F) warmer than the refrigerant circuit, forcing refrigerant to stay in the evaporator or condenser. The heater must be energized 12–24 hours prior to initial startup or after a power loss exceeding one hour to ensure proper lubrication and prevent flooded starts. This is critical for preventing premature compressor failure due to oil foaming and bearing wear.
Failed or missing heater leading to premature compressor failure due to oil foaming and bearing wear from diluted oil.
Refrigerant migration into the crankcase during shutdown, causing oil foaming, loss of lubricity, and scoring of bearings or rotor damage.
Flooded start where the compressor starts with liquid refrigerant in the oil, causing mechanical damage, valve breakage, or motor winding failure.