Danfoss 7773107 Belt Type Crankcase Heater – 65 W / 230 V | For SM/SZ 084-161

Danfoss 7773107 is a belt type crankcase heater wrapped externally around the compressor shell like a belt. It is rated at 65 W / 230 V and is specified for Danfoss SM/SZ 084-161 scroll compressors.

Heats the Sump Oil at Standstill — Prevents Liquid Slugging at Start-Up

When the compressor stops, refrigerant migrates to the coldest point of the system. This point is very often the compressor sump: the refrigerant condenses there and dissolves in the oil. Because the oil is thinned, it cannot perform its lubricating function.

When the compressor starts again, the pressure in the sump drops suddenly, the refrigerant dissolved in the oil boils off with foaming (oil foaming) and the oil pump delivers vapor. The result: dry friction in the bearings and, in severe cases, liquid slugging and a broken valve plate.

The crankcase heater breaks the first link in this chain — by keeping the oil warmer than the surroundings, it prevents refrigerant from condensing in the sump.

Technical Specifications (Official Danfoss Catalog)

• Brand / Code: Danfoss 7773107 (original code)
• Type: belt type, wrapped externally around the shell
• Power / Voltage: 65 W / 230 V
• Suitable compressors: Danfoss SM/SZ 084-161 series scroll compressors
• Certification: CE marking + UL
• Danfoss packaging: Multipack 6 (catalog information; sold as a single unit in this listing)

Other Voltage Options for the 65 W Body

• 🔧 Mounting position is critical: the heater is wrapped around the LOWER part of the compressor, where the oil collects — below the sight glass. A heater wrapped higher up does not heat the oil and wastes energy.
• ⚠️ Full contact is essential: the belt must rest against the shell along its entire length. Where a gap remains, the heater overheats itself and burns out. The clamp screw is tightened to a maximum of 2 Nm — overtightening crushes the belt.
• ⚠️ It is not self-regulating. Belt heaters are not self-regulating; they must be controlled externally. The correct wiring energizes the heater when the compressor STOPS (via the contactor auxiliary contact).
• Target: the sump oil should be kept about 10 K above the saturated low-pressure temperature of the refrigerant.
• Outdoors: below −5 °C and with wind above 5 m/s, additional thermal insulation of the compressor is recommended; otherwise the heater cannot keep up on its own.
• Check: A sound 65 W / 230 V heater should have a resistance of approximately 814 Ω (calculated as 230² ÷ 65). If the measurement shows an open circuit, the heating element is broken.
• Larger compressor? For SM/SZ 175-185, SH 180-485 and DSH 240-600 the 75 W 7773108 is used; for SY/SZ 240-380 the 130 W 7773122.