Service manual

T--318
4-- 8
4.10.3 Sequence of Operation -- Frozen Mode Cool-
ing
NOTES
1. In the Frozen Mode of operation the
evaporator motors run in low speed.
2. In low temperature ambients, the
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
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.
CONTROL TRANSFORMER
POWER TO
CONTROLLER
SIGNAL TO
CONTROLLER
SIGNAL TO
CONTROLLER
ENERGIZED
DE-ENERGIZED
FOR FULL DIAGRAM AND
LEGEND, SEE SECTION 7
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 degrees C
(0.4 degrees F) below 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 degrees C (0.4 degrees F) above set point and
the three minute off time has elapsed, relays TC and
TN are energizes to restart the compressor and con-
denser fan motors. The cool light is also illuminated.
4.10.4 Sequence of Operation -- Defrost
The defrost cycle may consist of up t o 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:
The manual defrost function (also manual defrost switch
function if equipped) is initiated and ended by the user
using the keypad or manual defrost switch (if equipped).
NOTE
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:
1 Depressing and holding the Defrost Interval key for
five seconds will initiate defrost. If the defrost interval
key is released in less than five seconds, defrost in-
terval (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. The controller probe diagnostic logic determines that
a probe check is necessary based on the tempera-
ture values currently reported by the supply and re-
turn probes.
5. The controller Demand Defrost configuration vari-
able (CnF40) is set to “In” and the unit has been in
pull down operation for over 2.5 hours without reach-
ing set point.
CONTROL TRANSFORMER
POWER TO
CONTROLLER
SIGNAL TO
CONTROLLER
SIGNAL TO
CONTROLLER
ENERGIZED
DE-ENERGIZED
FOR FULL DIAGRAM AND
LEGEND, SEE SECTION 7
SIGNAL TO
CONTROLLER
Figure 4-8 Defrost
The processing of a defrost request is controlled by the
defrost termination thermostat. The defrost termination
thermostat is not a physical component. It is a software
point that acts as a thermostat, allowing defrost when it
is considered “closed” and preventing or terminating
defrost when it is considered “open.” The actual
temperatures used to make the “open” or “closed”
determinations are dependent on the type of defrost
request made and the operator setting of configuration
variable CnF41. Configuration variable CnF41may be
factory set at the default value of 25.6 C (78 F) or a lower
valueof18C(64F).