Replace a Crankcase Heater (Compressor)

Replace a compressor crankcase heater (belly-band wrap or insertion-well type) that keeps the oil warm and drives refrigerant out of the crankcase to prevent migration / flooded starts (especially heat pumps and low-ambient cooling). Match the type/voltage/wattage, note whether it's always-on or contactor-controlled, energize it BEFORE restarting after a cold soak, and verify it actually warms.

Approx. 45 min

Before you start

•Confirmed the heater is the fault (open element, no heat, or signs of flooded starts / oil dilution / slugging) — a cold crankcase that won't warm with power applied.
•Heater type identified: belly-band (clamps around the compressor shell) vs insertion (slides into a well in the shell), and whether it is energized continuously (off the line) or only when the compressor is OFF (de-energized by the contactor).
•Matched replacement: correct shell diameter/well, voltage (120/240V or 24V types exist), and wattage band per the OEM.

Tools & materials

Multimeter (ohms for the element, voltage at the heater) · Clamp ammeter, nut drivers + screwdrivers · High-temp ties / clamp for the belly-band, anti-oxidant · Replacement crankcase heater (matched type/voltage/watt)

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Isolate & remove

Kill power and verify how it's controlled
Disconnect and verify power. Trace how the old heater is wired: many run continuously off the line so it stays warm even when the unit is off; some are energized only when the compressor contactor is open. Note this so the replacement is controlled the same way.
Tools: Multimeter
⚠ Lockout/tagout and verify 0 V — crankcase heaters are often live even with the contactor open.
Remove the old heater
For a belly-band: loosen the clamp and slide it off the lower shell. For an insertion type: pull it from the well. Note its exact location on the shell (low, over the oil sump) so the new one heats the oil, not the upper shell.

Fit the new heater

Mount the heater on the oil sump and wire it
Install the belly-band snug around the LOWER shell over the oil sump (or seat the insertion heater fully in its well) so it actually warms the oil. Wire it per the original control scheme (always-on line vs contactor-controlled), with a clean connection.
Tools: High-temp ties / clamp, Anti-oxidant
Target: Heater on the lower shell / fully seated in the well; wired to the same control scheme as removed

Energize, soak & verify

Energize and warm BEFORE restarting after a cold soak
After a cold soak, energize the crankcase heater and let it run several hours (per the maker, often a stated number of hours before first start) to boil refrigerant out of the oil. Starting a compressor with a flooded crankcase slugs liquid and oil and can break a compressor.
Target: Heater energized and crankcase warmed per the maker before the compressor restarts after a cold soak
⚠ Do not start a cold-soaked compressor with a flooded crankcase — pre-warm first to avoid slugging.
Confirm draw and that the shell warms
Measure the heater current/voltage and feel that the lower shell warms over time (warm to the touch, not hot). A heater drawing its rated watts and a warming sump confirm it's doing its job.
Tools: Clamp ammeter, Multimeter
Target: Heater draws ~rated watts; lower compressor shell is warm to the touch after soak time