5.8.2 Defrosting in general
The defrosting counteracts the icing-up of the evaporator during the normal controlled operation. The
evaporator is defrosted using additional heating of the evaporator (electric heater) or off-cycle defrosting.
Thereby, the temperature control of the refrigeration point is switched off. Defrosting functions differently in
single-zone or two-zone operation:
In two-zone operation, R1.1 determines the defrost termination of the first zone and R1.2 determines the
defrost termination of the second zone. However, in single-zone operation, the defrost termination of the
common first zone is not reached until both sensors have exceeded the defrost termination temperature; the
sensor R1.1 acts on heater 1, R1.2 (if plugged in) acts on heater 2:
R1.1: Defrost sensor (terminals Z31/Z32)
R1.2: Optional (terminals Z81/Z82)
E-valve 1: Relay for expansion valve 1 (terminals 23/24)
Defrost heater 1: Relay for defrost heater 1 (terminals 43/44)
Exception UR 141 NE / UR 141 TE:2nddefroststagefortheroomcontrollersinsingle-zoneoperation,see
description below.
Assignment of the sensors to the defrost relays
Optional not attached sensors are not used for switching the defrost relay.
Controller type Sensor Comment
UA 121 E, UA 131 E, UA 131 E LS, UA 141 E,
UR 141 NE, UR 141 TE, UK 100 E, KR 160 E
R1.1 Defrost relay 1
R1.2 Defrost relay 2
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