Crankcase heater – why it protects compressors

What a crankcase heater is, how it works, and features of a compressor heater

The crankcase heating belt — also known as a crankcase heater for compressors or a scroll compressor heater — is an electrical element that keeps the compressor above the refrigerant saturation temperature. This prevents refrigerant migration and oil dilution during off cycles. At start-up, non-diluted oil reduces friction, protecting bearings and moving parts, which improves reliability and lowers operating costs.

In heat pumps and chillers exposed to low ambient temperatures, a crankcase heater for compressors is often essential because it limits liquid slugging, hard starts, and mechanical stress typical of cold cycles. Therefore, it is a cornerstone of HVAC compressor protection, especially in systems operating in harsh climates or during extended stand-by periods.

How it works and why it is essential for heat pumps and chillers

The principle is simple: keep the compressor crankcase a few degrees above ambient temperature and above the refrigerant saturation temperature so condensation in the oil does not occur. In air-to-air and air-to-water systems, refrigerant migration during standstill is favored by cold spots; energizing the crankcase heater for compressors during off cycles — and in advance before restart — reduces condensation, prevents liquid carry-over damage, and improves start-up reliability.

Some models, such as a crankcase heater with a thermostat, automatically maintain the optimal oil temperature, increasing safety and start-up reliability.

Selection parameters

Choosing the right crankcase heater for compressors depends on:

• crankcase geometry (diameter/circumference),
• oil volume,
• refrigerant type, as saturation pressure sets the thermal threshold.

Heater power is sized according to heat losses (convection/radiation), contact surface, and compressor insulation; small crankcases typically start at a few tens of watts, with power increasing according to volume and exposure to cold. Contact quality is critical: a belt with a screw-type latch ensures uniform clamping, stable contact, and efficient heat transfer, simplifying installation and maintenance.

During installation, place the crankcase heater on the lower part of the crankcase (where refrigerant tends to accumulate), check insulation/IP rating, cable routing, and operating current. In cold climates, supply the heater sufficiently in advance to stabilize oil viscosity.

Crankcase heater features

A high-quality crankcase heater ensures uniform heat distribution. Its construction uses high-dielectric insulating materials and components designed to withstand repeated thermal cycles and vibration, preserving adhesion and the intended thermal profile.

The goal is proper heat transfer, achieving the power required to maintain ΔT, and preventing refrigerant migration into the oil during standstill, which can lead to dilution and loss of lubrication properties at start-up.

Continuous contact around the crankcase minimizes local temperature swings and mechanical stress, enabling smoother starts and reducing failures associated with liquid slugging. In HVAC systems with frequent on-off cycles, these features are crucial for effective compressor protection and better operational continuity.

Checks and maintenance

To ensure the crankcase heater works effectively:

• keep it energized during standstill,
• periodically check adhesion to the crankcase and cable integrity,
• monitor current draw.

For crankcase heaters with thermostats, check their response to temperature changes. Regular monitoring and early energizing before low-temperature start-ups prolong compressor life and reduce the risk of failures.

Two inspections per year are recommended — before and after the cold season. Long standstills require early energizing before restart.

Summary

A crankcase heater for compressors is a key element in protecting HVAC compressors in low temperatures. Thermostat-equipped versions additionally maintain optimal oil temperature automatically, improving start-up and minimizing wear. Using appropriate heaters increases system reliability and extends service life.