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cooling demand drops below -0.5°F or if any of the above con-
ditions turn false. If only a dehumidification demand exists and
the heat demand becomes greater than the Reheat Heat Set-
point Deadband (Setpoints
ing. The cooling mode can not officially end until all compres-
sors are off.
STAGING CONTROL
Once the unit is in a cooling mode, it must decide what the de-
mand is and how to satisfy it. If an economizer is installed and
can be used for cooling (Operating Modes
Yes), the unit will use it first (see economizer section for its oper-
ation). If the economizer can not be used or additional cooling is
needed, a mechanical cooling check is performed. OK to use
Compressors? (Operating Modes
set to yes when compressors are enabled and not locked out.
Based on the unit control configuration, requested cooling stages
(Run Status
COOL
REQ.C) will be determined then passed
to compressor control to actually add the cooling stages.
Thermostat Control
There are two ways of requesting stages when thermostat con-
trol is enabled, Traditional Thermostat control or Adaptive
control. Traditional Thermostat control is used if the Thermo-
stat Control Type (T.CTL) is set to 1, 2, or 3 and the economiz-
er is not available for free cooling. If Thermostat Control
(T.CTL) is set to 0 or any time the economizer is available for
free cooling, the unit will use Adaptive control for staging.
T.CTL = 0 (Adaptive Control)
Stage timers, Supply air trend, and supply air temperature lim-
its apply when determining the request for stages. The first re-
quest (REQ.C=1) comes immediately when the Y1 input is ac-
tive.
The
Cool
Stage
tion
COOL
C.INC) or the Cool Stage Decrease Time
(Configuration
COOL
er stage can be added or a stage can be subtracted. The Supply-
Air Trend (Operating Modes
next stage can be requested or should be subtracted based on
the Y2 input status. If the Y1 and Y2 inputs are dropped, the
supply air trend is not considered because cooling is no longer
needed. If at any time the Supply-Air Temperature (SAT) falls
below the Minimum Supply Air Temperature Upper Level
(Configuration
COOL
will not be allowed to increase. If at any time the SAT falls be-
low the Minimum Supply Air Temperature Lower Level (Con-
figuration
COOL
SAT
be reduced by one without honoring C.DEC. If SAT.L and
SAT.U are configured so that they are close together, the last
stage of compressor might cycle rapidly, slowed only by its
minimum on and off-time requirements.
T.CTL = 1 (1 Stage Y1) and T.CTL = 2 (2 Stage Y1)
Stage timers, Supply air trend, and supply air temperature lim-
its do not apply when determining the request for stages. Re-
quest staging will follow the thermostat inputs directly. Y1 will
request one stage. Y2 will request all stages.
T.CTL = 3 (Digital)
Stage timers, Supply air trend, and supply air temperature lim-
its do not apply when determining the request for stages. Re-
quest staging will follow the thermostat inputs directly. Y1 will
request one stage. Y2 will request two stages. Y1 and Y2 will
request all stages.
Space Sensor Control
Space sensor staging control is an adaptive anticipation control
that weighs the actual space demand against the trend of that
demand and the trend of the supply air. It also honors stage
time guards and supply air limits. The demand for cooling in
the space is displayed as the Cooling Demand (Run Sta-
tus
COOL
DMD.C). The control tries to anticipate the
change in the space because of its current stage status. This an-
ticipation is based on the Supply-Air Trend (Operating
RH.HB), the unit will end cool-
COOL
OK.EC=
COOL
OK.MC), will be
Increase
Time
(Configura-
C.DEC) has to expire before anoth-
COOL
SA.TR) decides if the
SAT
SAT.U), the requested stages
SAT.L), the requested stages will
Modes
COOL
SA.TR) and the Cool Demand Trend (Oper-
ating Modes
COOL
control how the space is reacting to the current running condi-
tions and help it decide when to add or remove one stage from
the requested stages. The Cool Stage Increase Time (Configu-
ration
COOL
C.INC) or the Cool Stage Decrease Time
(Configuration
COOL
er stage can be added or a stage can be subtracted. If at any
time the Supply-Air Temperature (SAT) falls below the Mini-
mum Supply Air Temperature Upper Level (Configura-
tion
COOL
SAT
SAT.U), the requested stages will not be
allowed to increase. If at any time the SAT falls below the Min-
imum Supply Air Temperature Lower Level (Configura-
tion
COOL
SAT
SAT.L), the requested stages will be re-
duced by one without honoring C.DEC. If SAT.L and SAT.U
are configured so that they are close together, the last stage of
compressor might cycle rapidly, slowed only by its minimum
on and off-time requirements.
COMPRESSOR CONTROL
The compressor control works hand and hand with the staging
control. As the staging control requests stages, the compressor
control determines what actual compressors are available or
running and tries to provide stages for what is requested. The
availability of a compressor depends on time guards, circuit di-
agnostics, outdoor temperature, and the unit size.
The Number of Circuits (Configuration
configuration tells the control how many compressors are in-
stalled on the unit. The Circuit A Lockout Temp (Configura-
tion
COOL
CIR.A
(Configuration
COOL
the outdoor temperature in which the respective compressor is
allowed to run down to. Timeguard A (Run Sta-
tus
COOL
CIR.A
tus
COOL
CIR.B
compressor has before it is available for use. Individual circuit
diagnostic tests are performed during operation which may or
may not allow a compressor to be used. The available stages at
any given time are displayed as Available Compressors (Run
Status
COOL
AVL.C). The actual compressors running at
any given time are displayed as Actual Cooling Stages (Oper-
ating Modes
COOL
tus
COOL
CIR.A
tus
COOL
CIR.B
spective compressor is running.
There are time guards to protect the compressors. Compressor
Min On Time (Configuration
pressor Min Off Time (Configuration
ply before a compressor can be turned back on or turned off.
OUTDOOR FAN CONTROL
Outdoor fans are controlled electro-mechanically, not directly
by the control system. Refer to specific unit wiring diagram
and or service manual for details on how the outdoor fans oper-
ate. In general, the outdoor fan is energized with compressor A
or may have partial fans operate with compressor B. Humidi-
MiZer units will have a Motormaster control on some or all
fans.
Heating Operation
The 48/50HC unit's heating operation consists of: demand,
mode determination, staging request to satisfy the demand, and
handling a request with the unit's resources. These resources
can be gas heat or electric heat. This section covers both gas
heat units and electric heat units. The Type of Heat Installed
(Configuration
HEAT
ry set to 1 for gas units, 2 for electric heat units with heaters in-
stalled, and 0 for electric heat units without heat installed. The
unit enters a heating mode based on a demand, decides how to
satisfy the demand, executes its plan, and then leaves the heat-
ing mode.
21
TRD.C). These trends will show the
C.DEC) has to expire before anoth-
COOL
CA.LO) and Circuit B Lockout Temp
CIR.B
CB.LO) configurations set
TG.A) and Timeguard B (Run Sta-
TG.B) display the time a respective
ACT.C). Compressor A (Run Sta-
CMP.A) and Compressor B (Run Sta-
CMP.B) are displayed on when the re-
COOL
MRT.C) and Com-
COOL
MOT.C) ap-
HT.TY) configuration will be facto-
N.CIR)
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Troubleshooting
