Danfoss 7773122 Belt-Type Crankcase Heater – 130 W / 230 V | For SY-SZ 240-380, SH 380, PSH 077

The Danfoss 7773122 is a belt-type crankcase heater wrapped around the outside of the compressor shell like a belt. When the compressor stops, refrigerant migrates to the crankcase, the coldest point in the circuit, and condenses in the oil. The heater prevents this migration by keeping the crankcase above the temperature of the oil.

Crankcase Heater That Protects the Compressor from Refrigerant Migration

In a system without a crankcase heater or with a faulty one, the oil is diluted by refrigerant; at the first start the oil foams, the oil film breaks down and bearing-piston wear begins. In severe cases liquid slugging destroys the compressor completely. For this reason, a crankcase heater is considered mandatory on all units installed outdoors and with long off-cycles — it is also a requirement in compressor warranties.

Technical Specifications (Official Danfoss Catalog)

• Brand / Code: Danfoss 7773122 (original spare part)
• Type: Belt-type crankcase heater
• Power: 130 W | Voltage: 230 V
• Certifications: CE + UL
• Compatible Compressors: Danfoss SY 240 / SY 300 / SY 380, SZ 240 / SZ 300 / SZ 380, SH 380, PSH 077
• Weight: ≈ 0.2 kg
• Other voltages of the same body: 110 V → 7773121 · 400 V → 7773123

• 🔧 Mounting height matters: The heater is wrapped around the compressor shell so that it sits just below the oil level — if fitted higher, it does not heat the oil and is ineffective.
• Make sure the belt is in full contact with the shell; if there is a gap, the heater overheats on itself and burns out.
• Commissioning: After a long shutdown, it is recommended that the heater be energized for at least 8-12 hours before starting the compressor. The heater is wired so that it is energized while the compressor is stopped and de-energized while it is running (via the contactor auxiliary contact).
• Check: The resistance of a sound 130 W / 230 V heater is approximately 400 Ω; if the measurement shows an open circuit, the heater has burned out.