Danfoss light commercial reciprocating compressors have a single-phase AC motor with built in motor protection (winding protector).
Most Danfoss compressors are designed with universal motors that can obtain high (HST) or low starting torque (LST) depending on the type of external electrics that are used.
Danfoss Motor Types:
RSIR: Resistant Start Induction Run (LST – low start torque)
CSIR: Capacitor Start Induction Run (HST – high start torque)
CSR: Capacitor Start Run (HST – high start torque)
RSIR motor types have a PTC start relay suitable for low starting torque (LST). The PTC relay requires the pressure in the system to be equalised before each start & a standstill period of 5 minutes to cool down before each start. The PTC relay (LST option) is normally used in well designed refrigeration systems with capillary tube.
CSIR motor types consist of a start relay & start capacitor for high starting torque (HST). Normally used in systems fitted with expansion valves or capillary tube were pressure equalisation is not obtained during the compressor standstill period.
CSR motor types consist of a start relay, start capacitor & run capacitor for high starting torque (HST). This starting (HST) option is mandatory for some of the larger Danfoss compressors.