Service manual

3−6T-362
Two timers are activated during dehumidification to pre-
vent rapid cycling and consequent contactor wear:
1. Heater debounce timer (three minutes) - The heater
debounce timer is started whenever the heater
contactor status is changed. The heat contactor re-
mains energized (or de-energized) for at least three
minutes even if the set point criteria are satisfied.
2. Out-of-range timer (five minutes) - The out-of-range
timer is started to maintain heater operation during a
temporary out-of-range condition. If supply air tem-
perature remains outside of the user selected
in-range setting for more than five minutes, the heat-
ers will be de-energized to allow the system to recov-
er. The out-of-range timer starts as soon as temper-
ature exceeds in-range tolerance value set by Cd30.
3.3.9 Perishable Dehumidification - Bulb Mode
Bulb mode is an extension of dehumidification which
allows changes to the evaporator fan speed and/or
defrost termination set points.
Bulb mode is active when Cd35 is set to “Bulb.” Once
bulb mode is activated, the user may then change
dehumidification evaporator fan operation from the
default (speed alternates from low to high each hour) to
constant low or constant high speed. This is done by
toggling Cd36 from its default of “alt” to “Lo” or “Hi” as
desired. If low speed evaporator fan operation is
selected, this gives the user the additional capability of
selecting dehumidification set points from 50 to 95%.
In addition, if bulb mode is active, Cd37 may be set to
override the previous defrost termination thermostat
(DTT) settings. The temperature at which the DTT will
be considered “open” may be changed [in 0.1C (0.2F)
increments] to any value between 25.6C (78F) and
4C (39.2F). The temperature at which the DTT is
considered closed for interval timer start or demand
defrost is 10C (50F) for “open” values from 25.6C
(78F) down to a 10C (50F) setting. For “open” values
lower than 10C, the “closed” values will decrease to the
same value as the “open” setting. Bulb mode is
terminated when:
1. Bulb mode code Cd35 is set to “Nor.”
2. Dehumidification code Cd33 is set to “Off.”
3. The user changes the set point to one that is in the
frozen range.
When bulb mode is disabled by any of the above condi-
tions, evaporator fan operation for dehumidification
reverts to “alt” and the DTS termination setting resets to
the value determined by CnF41.
3.3.10 Perishable Economy
Economy fan mode is an extension of the Perishable
Mode, and is provided for power saving purposes. Eco-
nomy fan mode is activated when Cd34 (also used for
Frozen Economy Mode) is set to “ON.” Economy fan
mode is used in the transportation of temperature-toler-
ant cargo or non-respiration items which do not require
high airflow for removing respiration heat.
There is no active display that indicates that economy
fan mode has been initiated. To check for economy fan
mode, perform a manual display of Cd34.
In order to initiate economy fan mode, a perishable set
point must be selected prior to activation. When econ-
omy fan mode is active, the evaporator fans will be con-
trolled as follows:
At the start of each cooling or heating cycle, the
evaporator fans will run in high speed for three
minutes. They will then be switched to low speed any
time the supply air temperature is within +/- 0.2C
(0.36F) of the set point and the return air temperature
is less than or equal to the supply air temperature
+3C (5.4F). The fans will continue to run in low
speed for one hour. At the end of the hour, the
evaporator fans will switch back to high speed and the
cycle will be repeated. If bulb mode is active, economy
fan mode will be overridden.
3.3.11 Perishable Mode Cooling - Sequence of
Operation
NOTE
In Standard Perishable Mode, the evaporator
motors run in high speed. In Economy Fan
Mode, the fan speed is varied.
a. When supply air temperature is above set point and
decreasing, the unit will cool with the condenser fan
motor (CF), compressor motor (CH), and evaporator
fan motors (EF) energized, and the white COOL light
illuminated. (See Figure 3−6). Also, if current or
pressure limiting is not active, the controller will close
contacts TS to open the economizer solenoid valve
(ESV) and place the unit in economized operation.
24 VOLT POWER
ENERGIZED
DE-ENERGIZED
TN
ST
F
HPS
CH
IP-CM
TC
CF
TE
IP-EM1
EF
IP-EM2
HTT
TH
HR
ESV
TS
TV
EF
ES
Figure 3−6 Perishable Mode Cooling
b. When supply air temperature decreases to a prede-
termined tolerance above set point (Cd30), the green
IN RANGE light is illuminated.
c. As air temperature continues to fall, unloaded cooling
starts (DUV pulses opens) as the supply air temper-
ature approaches set point. (See Figure 3−5).
d. When unloaded cooling starts, EEV control will trans-
ition from a full cool superheat set point to a lower
modulated cool superheat set point. Once unloading
starts, the EEV controls evaporator superheat based
on the system duty cycle where instantaneous super-
heat will vary.