5326602-XIM-B-1019
50
Johnson Controls Ducted Systems
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 38 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.
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 IGNITION CONTROL FLASH CODES
Table 38.
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 32 for the required gas heat
anticipator setting.
Table 31: Gas Heat Limit Settings
1
1.Rollout = 300°F (148.9°C), Auxiliary Limit = 200°F (93.3°C)
Unit
Main Limit Setting
Size
Opt.
Natural Gas
LPG
ZF120
N18
195°F (90.5°C)
195°F (90.5°C)
N24
150°F (65.6°C)
150°F (65.6°C)
ZF150
N18
195°F (90.5°C)
195°F (90.5°C)
N24
160°F (71.1°C)
160°F (71.1°C)
Table 32: Gas Heat Anticipator Setpoints
SETTING, AMPS
W1
W2
0.65
0.1