Carrier 69NT40-561-019 Operation And Service Manual Download Page 38

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T-359

4–12

Defrost may be initiated any time the defrost temperature sensor reading falls below the controller defrost termina-
mion thermostat set point. Defrost will terminate when the defrost temperature sensor reading rises above the defrost
termination thermostat set point. The defrost termination thermostat is not a physical component. It is a controller set-
ting that acts as a thermo stat, “closing” (allowing defrost) when the defrost temperature sensor reading is below the
set point and “opening” (terminating or preventing defrost) when the sensor temperature reading is above set point.
When the unit is operating in bulb mode (refer to

Section 4.3.11

), special settings may be applicable.

If the controller is programmed with the Lower DTT set ting option, the defrost termination thermostat set point may
be configured to the default of 25.6°C (78°F) or lowered to 18°C (64°F). When a request for defrost is made
through the manual defrost switch, communications or probe check the unit will enter defrost if the de frost tem-
perature thermostat reading is at or below the defrost termination thermostat setting. Defrost will terminate when
the defrost temperature sensor reading rises above the defrost termination thermostat setting. When a request for
defrost is made with the defrost interval timer or by demand defrost, the defrost temperature setting must be below
10°C (50°F).

When the defrost mode is initiated, the controller closes the EEV, opens contacts TC, TN, and TE (or TV) to de-
energize the compressor, condenser fan and evaporator fans. The COOL light is also de-energized. The controller
then closes contacts TH to supply power to the heaters. The defrost light is illuminated. When the defrost tempera-
ture sensor reading rises to the defrost termination thermostat setting, the de-icing operation is terminated.

Figure 4.10 Defrost

NOTE

The EEV and DUV are independently operated by the microprocessor. For full diagrams and legend,
see

Section 8

4.3.19

Defrost Pulsing

Pulse defrost logic periodically turns on the evaporator fans to circulate warm air around the drain line system, this
prevents water re-freezing during a defrost cycle.

To enable Defrost Pulsing, the user will scroll to Function Code 27, select “PuLs” and press the Enter key. Once
“PuLs” has been selected the user will then scroll to Function Code 60 and select the “Pulse Logic Set Point
Engagement Temperature”. The selections are from 0.0°C (32°F) to -18°C (0°F). At the selected Engagement set
point or below, “PuLs” will be active, and the evaporator fans may turn on. At set points above the selected
Engagement set point, “AUTO” defrost will be active.

NOTE

Default setting for “PuLs” is -18

C (0

F). The unit will reset to the default setting at the next PTI or Trip

Start.

The default defrost interval for “PuLs” will be every 6 hours. Defrost termination setting for “PuLs” is set to 20°C
(68°F).

24 VOLT POWER

ENERGIZED
DE--ENERGIZED

HPS

IP--CM

IP--EM1

IP--EM2