T-334
4--8
4.10.4 Sequence of Operation - Frozen Mode Cool-
ing
a. With supply air temperature above set point and de-
creasing, the unit will transition to economized cool-
ing with the condenser fan motor (CF), compressor
motor (CH), economizer solenoid valve (ESV), low
speed evaporator fan motors (ES) energized and the
COOL light illuminated. (See Figure 4--7.)
b.When the air temperature decreases to a predeter-
mined tolerance above set point, the in-range light is
illuminated.
24 VOLT POWER
ENERGIZED
DE-ENERGIZED
TN
USV
ST
F
PA
PB
HPS
TCP
PA
PB
IP--CM
TC
CF
TE
IP--EM
EF
IP--EM
HTT
TH
HR
TU
ESV
TS
XBSV
TT
LIV
TQ
TV
EF
ES
NOTE: High-speed, normal operation, single phase
evaporator fan shown. For three phase motor units,
the compressor is independently operated by an addi-
tional (CH) relay. For full diagrams and legend, see
Section 7.
Figure 4--7 Frozen Mode
c. When the return air temperature decreases to 0.2C
(0.4F) below set point, contacts TC, TS and TN are
opened to de-energize the compressor, economizer
solenoid valve and condenser fan motor. The cool
light is also de-energized.
d. The evaporator fan motors continue to run in low
speed to circulate air throughout the container. The
in-range light remains illuminated as long as the re-
turn air is within tolerance of set point.
e. If return air temperature drops to 10C (18F) or more
below set point, the evaporator fans are brought to
high speed.
f. When the return air temperature increases to 0.2C
(0.4F) above set point and the three minute off time
has elapsed, contacts TC, TS and TN are closed to
restart the compressor and condenser fan motor. The
cool light is illuminated.
4.10.5 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 initiated by any one of the following
methods:
1. The manual defrost function (also manual defrost
switch function if equipped) is initiated and ended by
the user through the use of the keypad or manual de-
frost 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 to
use this function.
Manual Defrost/Interval key operation:
Depressing and holding the Defrost Interval key for
five seconds will initiate defrost. If the defrost inter-
val key is released in less than five seconds, defrost
interval (code 27) shall be displayed.
2. The user sends a defrost command 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. If the controller is programmed with the Demand De-
frost option and the option is set to “IN” the unit will
enter defrost if it has been in operation for over 2.5
hours without reaching set point.
24 VOLT POWER
ENERGIZED
DE-ENERGIZED
TN
USV
ST
F
PA
PB
HPS
TCP
PA
PB
IP--CM
TC
CF
TE
IP--EM
EF
IP--EM
HTT
TH
HR
TU
ESV
TS
XBSV
TT
LIV
TQ
TV
EF
ES
NOTE: High-speed, normal operation, single phase
evaporator fan shown. For three phase motor units,
the compressor is independently operated by an addi-
tional (CH) relay. For full diagrams and legend, see
Section 7.
Figure 4--8 Defrost
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