Table of Contents
Advertisement
heating will continue. Once modified, the fan delay will not
change back to 45 seconds unless power is reset to the control.
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 for staged gas. For units equipped with modulating gas heat,
the second stage is controlled from the timer relay board (TR1).
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 fol-
lowed and the gas will remain on for a minimum of 1 minute.
Staged Gas Heat Board (SCB)
When optional staged or 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 sup-
ply-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 motor speed, and pro-
vides the main gas valve high fire input. When the start-up se-
quence 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 60.
Table 60 — TR1 Board LED Indicators
LED
DESIGNATION
ON
24 vac supplied to TR1
SR
Input received from IGC2, starts timer no. 1
Modulating Gas Valve modulated except during fixed output delay
MR
time
FR
IDM2 operates at high speed
CR
Modulating Gas Valve operates in high pressure stage
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 section.
The SC30 is powered by an output from the TR1. It receives a
capacity input from the SCB, provides a capacity output to the
modulating gas valve, and provides an output to the TR1 to de-
termine which state to command the induced-draft motor and
main gas valve. See Table 60.
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), regardless of the
unit size. The boards provide control for variable heating output
for the gas heat section.
Similar to the staged gas heat option, each IGC board is controlled
separately. The IGC functions are not affected by the modulating
gas control logic. When a call for gas heat is initiated, W on the
IGC board and the timer relay board (TR1) are energized. The
LED on TR1 board will be turned on. See Table 60 for LED
explanation.
When TR1 receives 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 conditioner 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 re-
ceive a capacity input from the SCB board and continuous modu-
late the heat output until the mode selection sensor is satisfied.
RESULT/ACTION
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 fol-
lowed and the gas will remain on for a minimum of 1 minute.
RELOCATE SAT FOR HEATING-LINKAGE APPLICATIONS
If Configuration
HEAT
temperature thermistor (Temperatures
relocated downstream of the installed heating device. This only
applies to two-stage gas or electric heating types (Configura-
tion
HEAT
HT.CF=1 or 2).
Determine a location in the supply duct that will provide a fairly
uniform airflow. Typically this would be a minimum of 5 equiva-
lent 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 two-wire conductor cable from the control box through
the low voltage conduit into the space inside the building and
route the cable to the new sensor location.
Installing a New Sensor
Use a duct-mount temperature sensor (Carrier P/N 33ZCSENPAT
or equivalent 10,000 ohms at 25C NTC [negative temperature co-
efficient] sensor). Install the sensor through the side wall of the
duct and secure.
Reusing the Factory SAT Sensor
The factory sensor is attached to the left-hand side of the supply
fan housing. Disconnect the sensor from the factory harness. Fab-
ricate 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 terminate
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 termi-
nals inside the control box.
TEMPERING MODE
In a vent or cooling mode, the economizer at minimum position
may send extremely cold outside air down the ductwork of the
building. Therefore, it may be necessary to bring heat on to coun-
teract 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 dis-
play under Setpoints:
ITEM
EXPANSION
T.PRG Tempering Purge SASP
T.CL
Tempering in Cool Offset
Tempering Vent
T.V.OC
Occ SASP
Tempering Vent
T.V.UN
Unocc. SASP
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. Secondly,
the tempering mode is only allowed when the rooftop is config-
ured for staged gas, modulating gas, SCR electric heat, or hydron-
ic heating (Configuration
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 control is in a sit-
uation where the economizer must maintain a minimum position/
71
LAT.M is set to YES, the supply air
AIR.T
SAT) must be
RANGE UNITS CCN POINT DEFAULT
–20 to 80
dF
TEMPPURG
5 to 75
^F
TEMPCOOL
–20 to 80
dF
TEMPVOCC
–20 to 80
dF
TEMPVUNC
HEAT
HT.CF=3 or 4). Also, if
50
5
65
50
Advertisement
Table of Contents
Troubleshooting
