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MM
2
1
MM
4
3
Economizer Mechanical Cooling Delay — This type of me-
chanical cooling delay is relevant to the all machine control
types.
If the economizer is able to provide free cooling at the start
of a cooling session, the mechanical cooling algorithm checks
the
economizer's
current
ECON
ECN.P) and compares it to the economizer's maxi-
mum position (Configuration
Once the economizer has opened beyond this point a
2.5-minute timer starts. If the economizer stays beyond this
point for 2.5 minutes continuously, the mechanical cooling
algorithm is allowed to start computing demand and stage
compressors.
Economizer Control Point (Run Status
— There are 4 different ways to determine the economizer
control point when the economizer is able to provide free
cooling:
If no mechanical cooling is active and HVAC mode = LOW
COOL
EC.C.P = Setpoints
SA.LO + Inputs
If no mechanical cooling is active and HVAC mode = HIGH
COOL
EC.C.P = Setpoints
SA.HI + Inputs
WITHOUT MOTORMASTER OPTION
60 Ton MCHX
Controlling Output
Circuit
Software
Board
A
CONDFANA
MBB Rly 6
A
CMPA1/A2
MBB Rly 3/4
B
CONDFANB
MBB Rly 5
B
CMPB1/B2
MBB Rly 1/2
Circuit A
# of Fans ON
Stage 1
OFC3
Stage 2
OFC3,4
When CMPA1 or CMPA2 staged ON, OFC3 on due to AUX
contactor
Stage up occurs if SCTA > HPSP or OAT > 75
Stage down occurs if SCTA < HPSP - 40 for two minutes and
OAT < 73
If the SCTA sensor has failed, then the control defaults to control based on the OAT sensor and turns on CONDFANA when the
ambient is above 65 dF and off when the ambient temperature is below 50 dF. If the SCTA and OAT sensors have all failed then the
control turns on CONDFANA when any compressor is on.
If the SCTB sensor has failed, then the control defaults to control based on the OAT sensor and turns on CONDFANB when the
ambient is above 65 dF and off when the ambient temperature is below 50 dF. If the SCTB and OAT sensors have all failed then the
control turns on CONDFANB when any compressor is on.
WITH MOTORMASTER OPTION
60 Ton MCHX
Controlling Output
Circuit
Software
Board
A
CONDFANA
MBB Rly 6
A
MM_A_RUN
SCB Relay 1
B
CONDFANB
MBB Rly 5
B
MM_B_RUN
SCB Relay 2
Circuit A
# of Fans ON
Stage 1
MM3
Stage 2
MM3, OFC4
Stage 2 starts with MM_A_VFD / MM_B_VFD at 50%, then modulates to control HP setpoint
Stage up occurs if SCTA > HPSP or OAT > 75
Stage down occurs if SCTA < HPSP - 40 for two minutes and
OAT < 73
Stage down starts with MM_A_VFD at 50%, then modulates to control HP setpoint
If the SCTA sensor has failed, then the control defaults to control based on the OAT sensor and turns on CONDFANA when the
ambient is above 65 dF and off when the ambient temperature is below 50 dF. If the SCTA and OAT sensors have all failed then the
control turns on CONDFANA when any compressor is on.
If the SCTB sensor has failed, then the control defaults to control based on the OAT sensor and turns on CONDFANB when the
ambient is above 65 dF and off when the ambient temperature is below 50 dF. If the SCTB and OAT sensors have all failed then the
control turns on CONDFANB when any compressor is on.
Fig. 9 — Outdoor Fan Staging Sequence (cont)
position
(Run
Status
ECON
EC.MX) – 5%.
VIEW
EC.C.P)
RSET
SA.S.R
RSET
SA.S.R
Contactor
OFM(s)
Conrolled
Controlled
OFC4
OFM4
OFC3
OFM3
OFC2
OFM2
OFC1
OFM1
Fans ON
Circuit B
1
OFM3
Stage 1
2
OFM3,4
Stage 2
When CMPB1 or CMPB2 staged ON, OFC1 on due to AUX contactor
Stage up occurs if SCTB > HPSP or OAT > 75
Stage down occurs if SCTB < HPSP - 40 for two minutes and OAT <
73
Contactor
OFM(s)
Conrolled
Controlled
OFC4
OFM4
n/a
OFM3
OFC2
OFM2
n/a
OFM1
Fans ON
Circuit B
1
OFM3
Stage 1
2
OFM3,4
Stage 2
Stage up occurs if SCTB > HPSP or OAT > 75
Stage down occurs if SCTB < HPSP - 40 for two minutes and OAT <
73
When the first stage of mechanical cooling has started
EC.C.P = 53 F plus any economizer suction pressure reset
applied
When the second stage of mechanical cooling has started
EC.C.P = 48 F plus any economizer suction pressure reset
applied
Heating Control —
system offers control for 3 different types of heating systems to
satisfy general space heating requirements: 2-stage gas heat, 2-
stage electric heat and multiple-stage (staged) gas heat.
Variable air volume (VAV) type applications (C.TYP = 1, 2,
3, or 5) require that the space terminal positions be commanded
to open to Minimum Heating positions when gas or electric
heat systems are active, to provide for the unit heating
system's Minimum Heating Airflow rate.
For VAV applications, the heat interlock relay (HIR) func-
tion provides the switching of a control signal intended for use
by the VAV terminals. This signal must be used to command
the terminals to open to their Heating Open positions. The HIR
is energized whenever the Heating mode is active, an IAQ
pre-occupied force is active, or if fire smoke modes, pressuriza-
tion, or smoke purge modes are active.
47
Logic
Comp A1 or A2 ON (Compressor AUX contactor)
Comp B1 or B2 ON (Compressor AUX contactor)
# of Fans ON
Fans ON
OFC1
1
OFM1
OFC1,2
2
OFM1,2
Logic
Comp A1 or A2 ON, speed Via MM_A_VFD
Comp B1 or B2 ON, speed Via MM_B_VFD
# of Fans ON
Fans ON
MM1
1
OFM1
MM1, OFC2
2
OFM1,2
The A Series ComfortLink control
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