Economizer Integration With Mechanical Cooling; Heating Control; Setting Up The System - Carrier 48AJ Operating And Service Manual

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
relay B and turn back on relay A.
Failure Mode Operation — If either of the SCT sensors fails,
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 58 — Condenser Fan Staging
FAN RELAY
020-035
OFC1
OFM1
(RELAY 6)
OFC2
OFM2
(RELAY 5)
ECONOMIZER INTEGRATION WITH MECHANICAL
COOLING — When the economizer is able to provide free
→
cooling (Run Status ECON
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
ITEM EXPANSION
HEAT HEATING CONFIGURATION
HT.CF Heating Control Type
HT.SP Heating Supply Air Setpt
OC.EN Occupied Heating Enabled
LAT.M MBB Sensor Heat Relocate
G.FOD Fan Off Delay, Gas Heat
E.FOD Fan Off Delay, Elec Heat
SG.CF STAGED GAS CONFIGS
HT.ST Staged Gas Heat Type
CAP.M Max Cap Change per Cycle
M.R.DB S.Gas DB min.dF/PID Rate
S.G.DB St.Gas Temp. Dead Band
RISE Heat Rise dF/sec Clamp
LAT.L LAT Limit Config
LIM.M Limit Switch Monitoring?
SW.H.T Limit Switch High Temp
SW.L.T Limit Switch Low Temp
HT.P Heat Control Prop. Gain
HT.D Heat Control Derv. Gain
HT.TM Heat PID Rate Config
*Some defaults are model number dependent.
48/50A UNIT SIZE
040-050 060
OFM1,
OFM1, OFM2
OFM2
OFM3, OFM3, OFM4,
OFM4 OFM5, OFM6
→
ACTV = YES), mechanical
Table 59 — Heating Configuration
the economizer's
→
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
If no mechanical cooling is active and HVAC mode = HIGH
COOL
EC.C.P = Setpoints
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 —
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 59.
RANGE UNITS
0 - 3
80 - 120 dF
Yes/No
Yes/No
45 - 600 sec
10 - 600 sec
0 - 4
5 - 45
0 - 5
0 - 5 ^F
0.05 - 0.2
0 - 20 ^F
Yes/No
110 - 180 dF
100 - 170 dF
0 - 1.5
0 - 1.5
60 - 300 sec
47
current position (Run
→ →
ECON EC.MX) – 5%.
→ →
VIEW
→ → →
SA.LO + Inputs RSET
→ → →
SA.HI + Inputs RSET
The A Series ComfortLink™ con-
CCN POINT DEFAULT
HEATTYPE 0*
SASPHEAT 85
HTOCCENA No
HTLATMON No
GAS_FOD 45
ELEC_FOD 30
HTSTGTYP 0*
HTCAPMAX 45*
HT_MR_DB 0.5
HT_SG_DB 2
HTSGRISE 0.06
HTLATLIM 10
HTLIMMON Yes
HT_LIMHI 170*
HT_LIMLO 160*
HT_PGAIN 1
HT_DGAIN 1
HTSGPIDR 90
→
Status
EC.C.P)
SA.S.R
SA.S.R
→