5566228-BIM-A-0818
Johnson Controls Ducted Systems
51
voltage is no longer sensed at the GV, the UCB will de-energize
the indoor blower following the elapse of the fan off delay for
heating.
If voltage has been sensed at the GV for at least 15 seconds
during the fan on delay for heating and GV voltage or “W1” is
lost, the indoor blower is forced on for the length of the fan off
delay for heating.
During a call for heat, if the UCB does not sense voltage at the
GV for a continuous five-minute period the UCB will initiate a
error message. The indoor blower motor will not be locked-on
while there is no GV voltage.
Safety Controls
The UCB monitors the temperature limit switch of gas heat
units.
The control circuit includes the following safety controls:
Limit Switch (LS)
This control is located inside the gas heat compartment and is
set to open at the temperature indicated in Table 10. It resets
automatically. The limit switch operates when a high
temperature condition, caused by inadequate supply air flow
occurs, thus shutting down the heater and energizing the
blower.
Auxiliary Limit Switch (ALS)
This control is located inside the blower compartment and is set
to open at a temperature of 200°F. It is reset manually. The limit
switch operates when a high temperature condition, caused by
inadequate supply air flow occurs, thus shutting down the
heater and energizing the blower.
The auxiliary limit switch is wired in series with the limit switch.
As such, the UCB cannot distinguish the auxiliary limit and the
gas heat limit switch operation except the auxiliary is manual
reset. Consequently, the control will respond in the same
manner as outlined above under “Limit Switch”.
The ICB monitors the Pressure and Rollout switches of gas
heat units.
The control circuit includes the following safety controls:
Pressure Switch (PS)
Once the draft motor has reached full speed and closes the
pressure switch during a normal ignition sequence, if the
pressure switch opens for 2 seconds, the GV will be de-
energized, the ignition cycle is aborted, and the ICB flashes the
appropriate code. See Table 31 Ignition Control Flash Codes.
The draft motor is energized until the pressure switch closes or
“W1” is lost.
Rollout Switch (ROS)
The rollout switch is wired in series with the pressure switch. As
such, the ICB cannot distinguish the rollout switch operation
from that of the pressure switch.
Consequently, the control will only respond in the same manner
as outlined above under “Pressure Switch”. An open rollout will
inhibit the gas valve from actuating.
The rollout switch opens at 300°F and is a manual reset.
Internal Microprocessor Failure
If the ICB detects an internal failure, it will cease all outputs,
ignore inputs, and display the proper flash code for control
replacement. The ICB remains in this condition until replaced.
Flash Codes
The ICB will initiate a flash code associated with errors within
the system. Refer to FLASH CODES FOR GAS HEAT
IGNITION CONTROL BOARD Table 31.
Resets
Remove the call for heating by lowering the thermostat setting
lower than the conditioned space temperature. This resets any
flash codes.
Gas Heat Anticipator Setpoints
It is important that the anticipator setpoint be correct. Too high
of a setting will result in longer heat cycles and a greater
temperature swing in the conditioned space. Reducing the
value below the correct setpoint will give shorter “ON cycles
and may result in the lowering of the temperature within the
conditioned space. Refer to Table 26 for the required gas heat
anticipator setting, for electronic thermostats refer to thermostat
manufacturer’s installation instructions.
Start-Up (Cooling)
Prestart Check List
After installation has been completed:
1.
Check the electrical supply voltage being supplied. Be sure
that it is the same as listed on the unit nameplate.
2.
Set the room thermostat to the off position.
3.
Turn unit electrical power on.
4.
Set the room thermostat fan switch to on.
5.
Check indoor blower rotation.
• If blower rotation is in the wrong direction. Refer to
Phasing Section in general information section.
Table 26: Gas Heat Anticipator Setpoints
SETTING, AMPS
W1
W2
0.65
0.1