Sequence Of Operation; Perishable Mode Heating; Sequence Of Operation -- Frozen Mode Cooling; Sequence Of Operation -- Defrost - Carrier 69NT40--541--200 TO 299 Operation And Service

4.10.2 Sequence Of Operation - -

Perishable Mode Heating

NOTE
The unit will heat only when in the Perishable
Mode, relay TH is electronically locked out
when in the Frozen Mode.
a. If the air temperature decreases 0.5_C (0.9_F) below
set point, the system enters the heating mode. (See
Figure 4-3). The controller closes contacts TH (see
Figure 4-6) to allow power flow through the heat ter-
mination thermostat (HTT) to energize the heaters
(HR). The HEAT light is also illuminated. The evapo-
rator fans continue to run to circulate air throughout
the container.
b. When the temperature rises to 0.2_C (0.4_F) below
set point, contact TH opens to de--energize the heat-
ers. The HEAT light is also de--energized. The evapo-
rator fans continue to run to circulate air throughout
the container.
c. A safety heater termination thermostat (HTT), at-
tached to an evaporator coil support, will open the
heating circuit if overheating occurs.
ENERGIZED
DE- -ENERGIZED
FOR FULL DIAGRAM AND
LEGEND, SEE SECTION 7
POWER TO
CONTROLLER
SIGNAL TO
CONTROLLER

Figure 4-6 Perishable Mode Heating

4.10.3 Sequence Of operation - - Frozen Mode
Cooling
NOTE
1. In the Frozen Mode of operation the
evaporator motors run in low speed.
2. In low temperature
condenser fan will be cycled by the
controller to maintain proper condensing
pressure.
a. With supply air temperature above set point and de-
creasing, the unit will be cooling with the condenser
fan motor (CF), compressor motor (CH), evaporator
T--317
CONTROL TRANSFORMER
SIGNAL TO
CONTROLLER
ambients the
fan motors (ES) energized and the COOL light illumi-
nated. (See Figure 4-7.)
b.When the air temperature decreases to a predeter-
mined tolerance above set point, the in-range light is
illuminated.
ENERGIZED
DE- -ENERGIZED
FOR FULL DIAGRAM AND
LEGEND, SEE SECTION 7
POWER TO
CONTROLLER
SIGNAL TO
CONTROLLER

Figure 4-7 Frozen Mode

c. Contacts TC and TN are opened to de-energize the
compressor and condenser fan motors when the re-
turn 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 re-
mains illuminated as long as the return air is within tol-
erance 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.
4.10.4 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).
Manual Defrost/Interval key operation:
Depressing and holding the Defrost Interval key for
five (5) seconds will initiate defrost. If the defrost in-
terval key is released in less than five (5) seconds,
defrost interval (code 27) shall be displayed.
2. The user sends a defrost request by communica-
tions.
3. The defrost interval timer (controller function code
Cd27) reaches the defrost interval set by the user.
4-8
CONTROL TRANSFORMER
SIGNAL TO
CONTROLLER