Specifications

41
Head Pressure Control Operation
— The following logic de-
scribes the head pressure control routine when any compressor
has been commanded on.
When the compressor has been commanded on, then con-
denser fan A will be energized (CD.F.A =ON). If the highest
active circuit SCT is above the HPSP, then condenser fan B
will be energized (CD.F.B =ON). If the OAT is above 75 F,
then both condenser fans A and B will be energized (CD.F.A =
ON and CD.F.B =ON). The fans will remain on until OAT
temperature drops below 73 F or the compressors are turned
off. If the SCT on an active circuit drops 40 F below the HPSP
for 2 minutes, then condenser fan B is turned off (CD.FB =
OFF).
NOTE: For size 60 units not configured for Motormaster®
control, the control stages down differently than the other
units. For size 60 units, the unit control will first turn off con-
denser fan relay A. After 2 minutes, the control will turn off
relayBandturnbackonrelayA.
Failure Mode Operation
—IfeitheroftheSCTsensorsfails,
then the control defaults to head pressure control based on the
OAT sensor. The control turns on CD.F.B when the ambient
temperature is above 65 F and turns off CD.F.B when the
ambient temperature is below 50 F. If the SCT and OAT
sensors have both failed, then the control turns on CD.F.B
when compressors are on.
Table 46 — Condenser Fan Staging
ECONOMIZER INTEGRATION WITH MECHANICAL
COOLING — When the economizer is able to provide free
cooling (Run Status
→ ECON → ACTV = YES), mechanical
cooling may be delayed or even held off indefinitely.
NOTE: Once mechanical cooling has started, this delay logic
is no longer relevant.
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 position (Run Status
→
ECON → ECN.P) and compares it to the economizer’s maxi-
mum position (Configuration → ECON → EC.MX)–5%.
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 → VIEW → EC.C.P)
— 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 → RSET → SA.S.R
If no mechanical cooling is active and HVAC mode = HIGH
COOL
EC.C.P = Setpoints
→ SA.HI + Inputs → RSET → SA.S.R
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 — The A Series ComfortLink™ con-
trol 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 Gas Heat.
Variable Air Volume (VAV) type applications (C.TYP =1,
2, 3, or 5) require that the space terminal positions be com-
manded 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, pressurization,
or smoke purge modes are active.
SETTING UP THE SYSTEM — The essential heating con-
figurations located at the local display under Configuration
→
HEAT. See Table 47.
Table 47 — Heating Configuration
*Some defaults are model number dependent.
FAN RELAY
48/50A UNIT SIZE
020-035 040-050 060
OFC1
(RELAY 6)
OFM1
OFM1,
OFM2
OFM1, OFM2
OFC2
(RELAY 5)
OFM2
OFM3,
OFM4
OFM3, OFM4,
OFM5, OFM6
ITEM EXPANSION RANGE UNITS CCN POINT DEFAULT
HEAT HEATING CONFIGURATION
HT.CF Heating Control Type 0 - 3 HEATTYPE 0*
HT.SP Heating Supply Air Setpt 80 - 120 dF SASPHEAT 85
OC.EN Occupied Heating Enabled Yes/No HTOCCENA No
LAT.M MBB Sensor Heat Relocate Yes/No HTLATMON No
G.FOD Fan Off Delay, Gas Heat 45 - 600 sec GAS_FOD 45
E.FOD Fan Off Delay, Elec Heat 10 - 600 sec ELEC_FOD 30
SG.CF STAGED GAS CONFIGS
HT.ST Staged Gas Heat Type 0 - 4 HTSTGTYP 0*
CAP.M Max Cap Change per Cycle 5 - 45 HTCAPMAX 45*
M.R.DB S.Gas DB min.dF/PID Rate 0 - 5 HT_MR_DB 0.5
S.G.DB St.Gas Temp. Dead Band 0 - 5 ^FHT_SG_DB 2
RISE Heat Rise dF/sec Clamp 0.05 - 0.2 HTSGRISE 0.06
LAT.L LAT Limit Config 0 - 20 ^FHTLATLIM 10
LIM.M Limit Switch Monitoring? Yes/No HTLIMMON Yes
SW.H.T Limit Switch High Temp 110 - 180 dF HT_LIMHI 170*
SW.L.T Limit Switch Low Temp 100 - 170 dF HT_LIMLO 160*
HT.P Heat Control Prop. Gain 0 - 1.5 HT_PGAIN 1
HT.D Heat Control Derv. Gain 0 - 1.5 HT_DGAIN 1
HT.TM Heat PID Rate Config 60 - 300 sec HTSGPIDR 90