Service manual

3-14T-294-01
3.1.6 Condenser Pressure Control (CPC)
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
temperatures.
In order for the CPC logic to be enabled, the following
conditions must be met:
S CPC configuration variable set to “In”
S CPT sensor is valid (alarm code AL68
inactive)
S AMBS sensor is valid
(alarm code AL57 inactive)
S AMBS is less than or equal to 26.6_C
(79.9_F)
S Voltage/Frequency ratio is less than or equal
to 8. 38
Whencondenserpressure control (CPC) is enabled (all
of the above conditions are met), either pressures or
timersmaydictateachangeofstatefromOFFtoON,or
ON to OFF . If the condenser fan i s OFF, it will be
energized if saturation condensing pressure is greater
than200psigORifthecondenserfanhasbeenOFFfor
amaximumofsixty seconds depending on theambient
temperature. If the condenser fan is ON, it will
de-energizeonlyifthesaturationcondensingpressureis
less than 130 psig and the condenser fan has been
running for a minimum of thirty seconds depending on
the ambient temperature. As the ambient temperature
increases, the amount of time that the condenser fan i s
energized will correspondingly increase.
If any one of the following conditions occur the CP C
logic will be disabled:
S CPT sensor is invalid
(alarm code AL68 activates)
S AMBS sensor is invalid
(alarm code AL57 activates)
S AMBS is greater than 29.5_C (85.1_F)
S Voltage/Frequency ratio is greater than 8.42
3.1.7 Controller Temperature Control
There are two control ranges, Frozen and Perishable
(chill). The Frozen range is active with set points at or
below --10_C(+14_F), or --5_C(+23_F) optionally,
and the Perishable range is active at set points above
-- 1 0 _C(+14_F), or --5_C(+23_F) optionally. See
Figure 3-5 and Figure 3-6.
The Controller configuration variable for “Heat
Lockout” (refer to Table 3-1) can be changed for set
points of either --10_C(+14_F), or --5_C(+23_F)
optionally.
NOTES
S Whenupwardsetpointchangesaremadeat
ambients below 27_C(80_F), the compressor
is immediately cycled OF F. The compressor
three minute time delay will be overridden, so
thatassoonasthecontroltemperatureisatleast
0.2_C(0.4_F ) above set point the compressor
will turn ON.
S At each manual power up of the unit, the
normallyclosed steppermotorSMVstartsata
6to21%openposition,andtheunitwillrunfor
three minutes to boil off dissolved refrigerant
fromthecompressoroil,dependingonambient
conditions.
S Depending on ambientconditions, theunit
maybe in apressurelimiting mode whichmay
restrict the maximum SMV position.
S Depending on the current limiting setting
and the environmental conditions, the SM V
position may be restricted.
3.1.7.1 Perishable (Chill) Range Above --10 _
__
_ C
(+14
_
__
_ F), or --5 _
__
_ C(+23 _
__
_ F) Optionally.
For set points above -- 1 0 _C(+14_F), or --5_C(+23_F)
optionally, theControllerm aintains SUPPLYair atthe
set temperature by the following modes of operation:
a. Operation in the conventional mode without
dehumidification (Code 33 OFF)
1. Atambientsbelow27_C(80_F), thecondenserfan
will cycle on/off depending on condenser pressure and
on/off times.
Ifthecondenserpressureisgreaterthan200psigORthe
condenser fan has been OFF at least 60 seconds, the
condenser fan will start.
Ifthe condenser pressureis lessthan130psig ANDthe
condenser fan remains ON for at least 30 seconds, the
condenser fan will stop.
2. At ambients above 27_C(80_F), condenser
pressure control (CPC) is disabled and the condenser
fan runs continuously.
If the unit starts when ambient is below --10_
__
_C
(+14_
__
_F) and condenser pressure is below 200 psig,
the condenser fan will not start until pressure
reaches 200 psig.