Sequence Of Operation - Defrost; Figure 5.7 Frozen Mode - Carrier 69NT40-541-001 Operation And Service

c. Contacts TC and TN are opened to de-energize the compressor and condenser fan motors when the return
air temperature decreases to 0.2°C (0.4°F) be low set point. The cool light is also de-energized.
d. The evaporator fan motors continue to run to circulate air throughout the container. The in-range light
remains illuminated as long as the return air is within tolerance of set point.
e. When the return air temperature increases to 0.2°C (0.4°F) above set point and the three minute off time
has elapsed, relays TC and TN are energizes to re start the compressor and condenser fan motors. The
cool light is also illuminated.
5.10.4

Sequence of Operation - Defrost

The defrost cycle may consist of up to three distinct operations. The first is de-icing of the coil, the second is a
probe check cycle and the third is snap freeze.
Defrost may be requested by any one of the following methods:
1. The manual defrost function (also manual defrost switch function if equipped) is initiated by the user.
Through the use of the keypad or manual defrost switch (if equipped).
The Manual Defrost / Interval key can be used to initiate a manual defrost. Minimum Software release
version #5126 is required in order for to use this function.
Manual Defrost/Interval key operation:
Depressing and holding the Defrost Interval key for five (5) seconds will initiate defrost. If the defrost
interval key is released in less than five (5) seconds, defrost interval (code 27) shall be displayed.
2. The user sends a defrost request by communications.
3. The defrost interval timer (controller function code Cd27) reaches the defrost interval set by the user.
4. The controller probe diagnostic logic determines that a probe check is necessary based on the temperature
values currently reported by the supply and return probes.
5. The controller Demand Defrost configuration variable (CnF40) is set to "In" and the unit has been in pull
down operation for over 2.5 hours without reaching set point.
T-316

Figure 5.7 Frozen Mode

ENERGIZED
DE-ENERGIZED
FOR FULL DIAGRAM AND
LEGEND, SEE SECTION 7
POWER TO
CONTROLLER
SIGNAL TO
CONTROLLER
NOTE
5–12
CONTROL TRANSFORMER
SIGNAL TO
CONTROLLER