Carrier 50PG20-28 Controls, Start-Up, Operation, Service And Troubleshooting Instructions page 42

Two methods are used to add and relnove stages of cooling
for units with more than one compressor. The first method
causes the unit to operate around its steady-state number of
stages. For example, if the correct number of stages is between
0 and 1, this method wilt cause the first stage to cycle. If the
correct number of stages is between 1 and 2, this method will
cause the second stage to cycle. The second method causes the
unit to find the steady-state nulnber of stages. Details of these
methods are provided below.
The control uses two methods to add a stage of compressor
cooling. The first method will add a stage of cooling when the
Cooling Delnand (Operating Modes _'OOL---_gPT--+
DMD. 0 plus the change in cool delnand (Operating
Modes4DOL_9Pr-+rm).() times the Cool Therlnal Lag
Factor (Operating Modes4DOL---_9PT4_.LA6) is greater
than the SPY Cool Demand (+) Level (Operating Modes_
cOOL _gPr _(_z.PO).
DMD.C+ rRD.C*
C.LAG> (Z.PD
This method is only used after the Compressor Settling
Time ((bnfiguration--_U?_gT--_qAT.I), has been exceeded
and the supply-air temperature is slowly increasing. The sec-
oM method will add a stage of cooling when Cool Demand is
greater than the SPT Cool Delnand (+) Level plus 0.5° F
(DMD.C > (Z.PD + 0.5) and the supply-air telnperature
(Operating Modes_,COOL--_AT--_AI) is changing at a
rate greater than 0.3 ° F per minute.
The control uses two methods to relnove a stage of com-
pressor cooling. The first method will relnove a stage of cool-
ing when the Cooling Demand (Operating Modes4DOL
_gPT_OMO.
_) plus
the change in cool demand (Operating
Modes4DOL---_qPT_TRD._) times the Cool Therlnal Lag
Factor (Operating Modes_OOL--_7PT_'.LAG) is less
than the SPY Cool Demand @) Level (Operating Modes_
COOL---_gPT4Z.ND).
DMD.C+ fRO.C*
C.LAG< (Z.ND
This method is only used after the Compressor Settling
Time (SAT.!), has been exceeded and the supply air tempera-
ture is slowly decreasing. The second method will relnove a
stage of cooling when Cool Demand is less than the SPY Cool
Demand @) Level minus 0.5° F (DMD.C < (Z.ND 0.5) and
the supply air telnperature (SA!) is changing at a rate less than
0.2° F per minute.
Configurable delays also apply when adding stages
((bnfiguration_COOL_.IN 0 or relnoving stages
((bnfiguration_COOL _.DE O. Compressor minimum
on-time (Configumtion_'COOL--_lIRT. 0 and minimum
off-time (Configuration _'OOL---_MOT..() also apply.
OUTDOOR FANS Each unit has a means for variable
outdoor airflow to control condenser pressure control within an
acceptable range by responding to varied operating modes and
alnbient temperatures. This is implemented dift_rently on
different units using multi-speed motors, multiple outdoor tans,
or variable-speed motor controllers.
NOTE: Factory default configurations account for these lnodel
ditthences and should not be changed. The default configura-
tions have been qualified over a lane range of conditions and
are provided in case a field replacement of a control board
occurs and the settings need to be checked or manually config-
ured. Outdoor fan operation is further described below to assist
in troubleshooting.
Units Without Humidi-MiZer
TM
System The outdoor fan
speed, number, and location for each of three levels is defined
tbr each cooling circuit in the Circuit submenus (Configura-
tion_COOL_CIR.x). Results of the factory configurations
are sho,a_ in Tables 38A-39B. The tan level selected during
operation is based on factory configurations of outdoor
temperature limits and condenser pressure limits. These are in
the Outdoor Fan Control submenu (Configuration--+
COOL _OF O. Initial thn level starts at zero and increments to
level 1when Fan LEV0 Max Pressure limit is reached. Chang-
es between levels 1 to 3 are initially selected based on outdoor
air temperature (OAT) input and the level On and Off tempera-
rare limits. The levels may be further adjusted based on the
circuit saturated condensing temperatures (Tempem-
tures--+REET--_7CT.x) and the level Max and Min pressure
limits.
Units With Humidi-MiZer System Outdoor tan control for
Humidi-MiZer units includes a Motonnaster,_a)variable-speed
control for OFM 1 and OFM4. Contactor OFC 1 controls power
to the Motonnaster control. The Motorlnaster control automat-
icalty adjusts the outdoor thn speed to maintain approximately
80 to 100 F condenser telnperature for circuit A at all outdoor
ambient temperatures. Contactor OFC2 controls the relnaining
two Pans (48/50PG20) or relnaining 4 _ans (48/50PG24 and
28). The tan level operation is detennined by some or all out-
door thn control configurations described above, plus addition-
at Humidilnizer confimlrations ((bnfiguration--->HZMR).
Table 38A -- Outdoor Fan Level Transitions
without Humidi-MiZer System
FAN LEVEL OUTDOOR TEMPERATURE (F)
Level 2 On 55 (size 20), 45 (sizes 24, 28)
Level 2 Off 50 (size 20), 40 (sizes 24, 28)
Level 3 On 65
Level 3 Off 55
Table 38B -- Outdoor Fan Level Transitions
with Humidi-Mizer System
FAN LEVEL OUTDOOR TEMPERATURE (F)
Level 2 On 88 (size 20), 8! (size 24 and 28)
Level 2 Off 57
Level 3 On 88 (size 20), 88 (size 24 and 28)
Level 3 Off 78 (size 20), 82 (size 24 and 28)
Table 39A -- Fan Level Control of Outdoor Fan
Contactors (1, 2, 3)without Humidi-MiZer System
FAN LEVEL
0
1
2
3
CIRCUIT
A B
1 (20, 24) 3
1,3 (28)
1,2 (20) 2, 3(20)
2 (24, 28) 2 (24, 28)
1,2 (20, 24) 1, 2, 3 (28) 2, 3
Table 39B -- Fan Level Control of Outdoor Fan
Contactors (1 and 2) with Humidi-Mizer System
FAN LEVEL CIRCUITS A and B
0
1 1
1,2 (20)
2 2 (24-28)
3 1,2
Gas Heating (48PG Units)--
For 48PG units, the
heat type confi_ration Configuration -+HEAT---_HT.. T Y will
be thctory set to a value of 1.
Heat will not operate if the outdoor temperature is
greater than the value configured for the heat lockout telnpera-
ture, (bnfiguration---yHEAT---yHT..LO. Minimum on-time,
Configumtion---yHEAT---yMRT.H, and lninilnum off-time,
Configulvttion---yHEAT---yMOT..H, tilnemmrds apply to both
stages of heating. Factory default values are 2 minutes On and
2 lninutes Off The IGC lninimum on-time of 1 lninute will be
followed even ifMRT.His lower and during Sel_:ice Test.
42