Service manual

4-4T-294-01
4.4.3 Cooling -- Controller Set BELOW --10
_
__
_ C
(+14
_
__
_ F), or --5 _
__
_ C(+23 _
__
_ F) optionally
NOTES
S The stepper motor suction modulation valve
(SMV) may be up to 100% open depending
on the current and pressure limiting controls.
S The evaporator motors run in low speed.
S The compressor runs in high speed.
When the return air temperature decreases to 0.2_C
(0.4_F)belowsetpoint, relaysTDandTNde-energize.
This results in de-energizing the compressor and
condenser fan motor. Also, the cool light is
de-energized. The evaporator fan m otors continue to
run to circulate air throughout the container.
When the return air temperature increases to 0.2_C
(0.4_F) above set point, and providing a sufficient
off-timeperiodhaselapsed, relays TDandTNenergize
torestartt hecompressorandcondenserfanmotor.Also
at this time, the cool light is illuminated.
4.4.4 Controller Set ABOVE --10 _
__
_ C(+14 _
__
_ F), or
-- 5
_
__
_ C(+23 _
__
_ F) optionally
a. Cooling Mode (See Figure 4-1.)
NOTES
S Evaporator fan motors will run in high speed.
(Contactor EF energized)
S A pressure control system has been
incorporated by means of a condenser
pressure transducer (CPT) and condenser
pressure control (CPC ) logic to maintain
discharge pressures above 130 psig in low
ambients.
S The condenser fan will cycle off if the
condenser pressure is below 130 psig. If the
condenser pressure goes above 200 psig, the
condenser fan will cycle on.
With supply air temperature decreasing, and if the
supply air is above set point, the unit will be cooling
with the condenser fan motor, compressor motor and
evaporatorfan motorsenergized. Also, at this time, the
cool light is illuminated.
When the air temperature decreases to a predetermined
tolerance above set point, relay TI energizes and the
in-range light is illuminated. (Refer to section 3.1.4,
Code 30.)
If the air temperature continues to fall, modulating
coolingstartsatapproximately2.5_C(4.5_F)aboveset
point.
During this cooling mode, a running sum of the
temperature differential (supply air temperature -- set
point)iskept.Whenthesupplyairfallsbelowsetpoint,
the differential is negative. The longer supply air
remains below set point, t he greater the negative
differential in the running sum.
When the supply airtemperature decreasesto 0. 2_Cor
morebelowsetpointandtherunningsumisgreaterthan
orequalto--250degreesCelsiusseconds,relaysTNand
TC de-energize shutting off the condenser fan and
compressormotors.Also,t hecoollightisde-energized.
NOTE
Forexample:Ifthetemperatureinthecontainer
box falls 1_C below set point for 250 seconds,
or any combination of t emperature and time
that equals 250 degrees Celsius seconds, t he
unit will shut off. (Formula: X_C times TIME
inseconds.WhereXistheamountofdegreesin
Celsius, i.e., 1_C times 250 seconds = 250
degrees Celsius seconds.)
The evaporator fan motors continue to run to circulate
airthroughoutthecontainer.Thei n-rangelightremains
illuminatedaslongasthesupplyairiswithinatolerance
of set point, and the 15 minute override is met.
If the unit is in the holding mode (neither heating nor
cooling) and the supply air temperature increases to
0.2_C(0.4_F) above set point, and providing a six
minute off time has elapsed, relay TC energizes to
restartthecompressor.Also,atthistime, thecondenser
fan m otor starts and the cool light is illuminated.