Service manual

3-17
T-294-01
3.1.7.2 Frozen Range Below --10
_
__
_ C(+14 _
__
_ F), or
-- 5
_
__
_ C(+23 _
__
_ F) Optionally
For setpoints below -- 1 0 _C(+14_F), or --5_C(+23_F)
optionally,theControllerm aintainsRETURNairatthe
set point temperature using the following modes of
operation:
a. Operation in the conventional mode
(Code 33 OFF)
The return air probe is used for control and is so
indicated by the LED on the display board.
The Frozen temperature rangeis not sensitive to minor
temperature changes. The method of temperature
control employed in this range takes advantage of this
facttogreatlyimprovetheenergyefficiencyoftheunit.
Temperature control in the Frozen range at or below
-- 1 0
_ C(+14 _ F), or --5_C(+23_F) optionally, is
accomplished by cycling the compressor on and off as
the load demand requires.
Ifthereturnairtemperatureinthecontainerdrops0.2_C
(0.4_F)belowt hesetpointtemperature,thecompressor
is cycled off. When the temperature is greater than
0.2_C(0.4_F) above the set point and the threeminute
time delay has been met, the compressor will restart.
The unit will always operate at full capacity, and the
stepper motor suction modulation valve (SMV) will
open to 100%, or as allowed by current and pressure
limiting.
NOTE
On start up of the unit, SMV will reset to a
known open position. This is accomplished by
assuming the valve was fully open, driving it
fully closed, resetting the percentage open to
zero, then opening to a known 21% staging
position. This makestheunit readyt o start and
normal operation will begin.
To prevent on/off cycling of t he compressor from
occurring, a three mi nute compressor off time must be
satisfied before the compressor will restart. Under a
condition of rapidly changing return air temperature,
the time delay may allow the return air temperature to
rise slightly more than 0.2_C(0.4_F) above the set
point temperature before the compressor can restart.
b. Operation in the economy mode (Code 34 OFF)
The economy mode is deactivated by setting function
code Cd34 to the “OFF” status. Economy mode has no
active display indicator to show that it is enabled, so a
manual display of function code Cd34 must be
performed to enable the user tosee its current status. A
second way to deactivate economy mode is to change
the set point. Once economy mode is deactivated, the
system will return to normal control mode operations.
In order to achieve economy m ode frozen operation, a
frozen setpointtemperaturemustbeselectedPRIORto
activatingeconomymode.Wheneconomymodefrozen
is active, the system will perform normal frozen mode
operations except that the entire refrigeration system,
excluding the Controller, will be turned off when the
controltemperatureislessthanorequaltothesetpoint--
2_C, (i. e., theset point is set at --11_Cand theoperator
subtracts --2_C, the result will equal --13_C). After an
off-cycleperiodof60minutes,theunitwillturnonhigh
speed evaporatorfansforthreeminutes,andthencheck
the control temperature. If the control temperature is
greater than or equal to the set point + 0.2_C., the unit
willrestarttherefrigerationsystemandcontinuetocool
until the previously mentioned off-cycle temperature
criteria are met. If the control temperature is less than
the set point + 0.2_C, the unit will turn off the
evaporatorfansand restartanother60 minuteoff-cycle.
c. Operation in the bulb mode (Code 35 OFF)
The unit will not run in bulb mode if a frozen rangeset
point isselected. As described in section3.1.7.1.d., ifa
frozen set point is selected, dehumidification is
deactivatedandthetemperatureabovewhichDTSmust
go during defrost resets to 25.6_C(78_F).
3.2 PRE- TRIP DIAGNOSTICS
CAUTION
Pre-trip inspection should notbeperformed
with critical temperature cargoes in the
container.
NOTE
When Pre-Trip is initiated, dehumidification
and bulb mode will be deactivated. At the
completion of Pre-Trip, dehumidification and
bulb mode must be turned back on again.
Pre-tripDiagnosticsisani ndependentm odewhichwill
suspend the normal Control Mode activities when
initiatedbytheuser.Withpre-tripdiagnostics,eitherall
the pre-trip tests can be executed in a defined sequence
(AutoMode),oroneofthepre-trip testscanbeselected
to be executed (Manual Mode), based on t he sequence
of key selections made.