68
Staged Gas Heat Board (SCB)
When optional modulating gas heat is used, the SCB board is
installed and controls additional stages of gas heat. The SCB
also provides additional sensors for monitoring of the supply-
air and limit switch temperatures. For units equipped with
modulating gas heat, the SCB provides the 4 to 20 mA signal
to the SC30 board that sets the modulating gas section capacity.
This board is located in the main unit control box.
Timer Relay Control Board (TR1)
The TR1 is used on modulating gas-heat-equipped units only.
It is located in the gas heat section and is used in combination
with the SC30 to provide control of the modulating gas heat
section. The TR1 receives an input from the IGC, initiates a
start-up sequence, powers the SC30, sets the induced-draft mo
-
tor speed, and provides the main gas valve high fire input.
When the start-up sequence is complete, the TR1 checks the
input from the SC30 to determine which state to command the
induced-draft motor and main gas valve. See Table 45.
Signal Conditioner Control Board (SC30)
The SC30 is used on modulating gas-heat-equipped units only.
It is located in the gas heat section and is used in combination
with the TR1 to provide control of the modulating gas heat sec
-
tion. The SC30 is powered by an output from the TR1. It re
-
ceives a capacity input from the SCB, provides a capacity out
-
put to the modulating gas valve, and provides an output to the
TR1 to determine which state to command the induced-draft
motor and main gas valve. See Table 45.
Table 45 —
TR1 Board LED Indicators
Modulating Gas Control Boards (SC30 and TR1) Logic
All gas modulating units are equipped with one timer relay
board (TR1) and one signal conditioner board (SC30), regard
-
less of unit size. The boards provide control for variable heat
-
ing output for the gas heat section.
Similar with staged gas heat option, each IGC board is con
-
trolled separately. The IGC functions are not affected by the
modulating gas control logic. When a call for gas heat is initi
-
ated, W on the IGC board and the timer relay board (TR1) are
energized. The LED on TR1 board will be turned on. See
Table 45 for LED explanation.
When TR1 received an input from the IGC board, the relay
board starts Timer no. 1 or start-up sequence: sets the gas valve
stage and the inducer motor speed, and enables the signal con
-
ditioner board SC30. During Timer no. 1, the SC30 board
keeps a fixed heating output. When Timer no. 1 expires, the
modulating gas control boards start Timer no. 2. Throughout
the duration of Timer no. 2, the boards determine which state
to adjust the capacity output to satisfy the heat demand. When
Timer no. 2 expires, the boards receive a capacity input from
the SCB board and continuously modulate the heat output until
the mode selection sensor is satisfied.
The IGC boards only control the first stage of gas heat on each
gas valve. The second stages are controlled directly from the
MBB board. The IGC board has a minimum on-time of
1 minute.
In modes such as Service Test where long minimum on times
are not enforced, the 1-minute timer on the IGC will still be
followed and the gas will remain on for a minimum of
1 minute.
RELOCATE SAT FOR HEATING-LINKAGE APPLICATIONS
If
Configuration
HEAT
LAT.M
is set to YES, the supply
air temperature thermistor (
Temperatures
AIR.T
SAT
)
must be relocated downstream of the installed heating device.
This only applies to 2-stage gas or electric heating types (
Con
-
figuration
HEAT
HT.CF
=1 or 2).
Determine a location in the supply duct that will provide a fair
-
ly uniform airflow. Typically this would be a minimum of 5
equivalent duct diameters downstream of the unit. Also, care
should be taken to avoid placing the thermistor within a direct
line-of-sight of the heating element to avoid radiant effects.
Run a new 2-wire conductor cable from the control box
through the low voltage conduit into the space inside the build
-
ing and route the cable to the new sensor location.
Installing a New Sensor
Procure a duct-mount temperature sensor (Carrier P/N
33ZCSENPAT or equivalent 10,000 ohm at 25°C NTC [nega
-
tive temperature coefficient] sensor). Install the sensor through
the side wall of the duct and secure.
Re-Using the Factory SAT Sensor
The factory sensor is attached to the left-hand side of the sup
-
ply fan housing. Disconnect the sensor from the factory har
-
ness. Fabricate a mounting method to insert the sensor through
the duct wall and secure in place.
Attach the new conductor cable to the sensor leads and termi
-
nate in an appropriate junction box. Connect the opposite end
inside the unit control box at the factory leads from MBB J8
terminals 11 and 12 (PNK) leads. Secure the unattached PNK
leads from the factory harness to ensure no accidental contact
with other terminals inside the control box.
TEMPERING MODE
In a vent or cooling mode, the economizer at minimum posi
-
tion may send extremely cold outside air down the ductwork of
the building. Therefore it may be necessary to bring heat on to
counter-effect this low supply-air temperature. This is referred
to as the tempering mode.
Setting up the System
The relevant set points for tempering are located at the local
display under
Setpoints
:
Operation
First, the unit must be in a vent mode, a low cool, or a high
cool HVAC mode to be considered for a tempering mode. Sec
-
ondly, the tempering mode is only allowed when the rooftop is
configured for modulating gas, SCR electric heat, or hydronic
heating (
Configuration
HEAT
HT.CF
=3 or 4). Also, if
OAT is above the chosen tempering set point, tempering will
not be allowed. Additionally, tempering mode is locked out if
any stages of mechanical cooling are present.
If the control is configured for staged gas, modulating gas,
SCR electric heat, or hydronic heating and the control is in a
vent, low cool, or high cool HVAC mode, and the rooftop con
-
trol is in a situation where the economizer must maintain a
LED
DESIGNATION
RESULT/ACTION
ON
24 VAC Supplied to TR1
SR
Input received from IGC2, starts timer no. 1
MR
Modulating Gas Valve modulated except during fixed
output delay time
FR
IDM2 operates at high speed
CR
Modulating Gas Valve operates in high pressure stage
ITEM EXPANSION RANGE UNITS
CCN
POINT
DEFAULT
T.PRG
Tempering
Purge
SASP
–20-80
dF
TEMPPURG
50
T.CL
Tempering
in Cool
Offset
5-75
^F
TEMPCOOL
5
T.V.OC
Tempering
Vent
Occ SASP
–20-80
dF
TEMPVOCC
65
T.V.UN
Tempering
Vent
Unocc.
SASP
–20-80
dF
TEMPVUNC
50
Содержание WeatherExpert 48N2
Страница 135: ...135 Fig 18 48 50N Typical Power Schematic Nominal 075 Ton Unit Shown ...
Страница 136: ...136 Fig 19 48 50N Typical Power Schematic Nominal Ton 90 150 Units Shown ...
Страница 137: ...137 Fig 20 48 50N Main Base Board Input Output Connections ...
Страница 138: ...138 Fig 21 48 50N RXB EXB CEM Input Output Connections a48 9307 ...
Страница 139: ...139 Fig 22 48 50N EXV SCB Input Output Connections a48 9308 ...
Страница 140: ...140 Fig 23 48N Typical Modulating Gas Heat Unit Control Wiring ...
Страница 141: ...141 Fig 24 50N Typical Electric Heat Unit Control Wiring ...
Страница 144: ...144 Fig 27 48N Typical Gas Heat Section Wiring Nominal Ton 120 to 150 Units ...
Страница 145: ...145 Fig 28 48 50N Typical Power Component Control Wiring 460 v ...
Страница 146: ...146 Fig 29 48 50N Component Control Wiring 575 v Nominal Ton 075 to 150 Units ...
Страница 147: ...147 Fig 30 48 50N Component Arrangement Power Box ...
Страница 148: ...148 Fig 31 48 50N Component Arrangement Control Box ...
Страница 168: ...168 Fig 47 Sensor and Ignition Position Fig 48 Combustion Blower Details SENSOR DETAILS IGNITION DETAILS ...
Страница 240: ...240 APPENDIX D VFD INFORMATION CONT Fig G VFD Bypass Wiring Diagram WHEN USED ...