66389-BIM-C-1208
Johnson Controls Unitary Products
35
energize the blower motor. If the second stage of
heat is required, heater relay (RB) will be energized.
After completing the specified fan on delay for heat-
ing, the UCB will energize the blower motor.
b.
The thermostat will cycle the electric heat to satisfy
the heating requirements of the conditioned space.
ELECTRIC HEATING OPERATION ERRORS
TEMPERATURE LIMIT
If the UCB senses zero volts from the high temperature limit,
the indoor blower motor is immediately energized.
This limit is monitored regardless of unit operation status, i.e.
the limit is monitored at all times.
If the temperature limit opens three times within one hour, it
will lock-on the indoor blower motor and a flash code is initi-
ated (See Table 29).
SAFETY CONTROLS
The UCB monitors the temperature limit switch of electric
heat units.
The control circuit includes the following safety controls:
LIMIT SWITCH (LS)
This control is located inside the heater compartment and is
set to open at the temperature indicated in the Electric Heat
Limit Setting Table 23. It resets automatically. The limit switch
operates when a high temperature condition, caused by inad-
equate supply air flow occurs, thus shutting down the heater
and energizing the blower.
FLASH CODES
The UCB will initiate a flash code associated with errors
within the system. Refer to UNIT CONTROL BOARD FLASH
CODES Table 29.
RESET
Remove the call for heating by lowering the thermostat set-
ting lower than the conditioned space temperature.This
resets any flash codes.
ELECTRIC 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 24 for the required electric
heat anticipator setting.
GAS HEATING SEQUENCE OF OPERATIONS
When the thermostat calls for the first stage of heating, the
low-voltage control circuit from “R” to “W1” is completed. A
call for heat passes through the UCB to the ignition control
board (ICB). The UCB monitors the “W1” call and acts upon
any call for heat by monitoring the gas valve (GV). Once volt-
age has been sensed at the GV, the UCB will initiate the fan
on delay for heating, energizing the indoor blower the speci-
fied delay has elapsed.
When the thermostat has been satisfied, heating calls are
ceased. The GV is immediately closed. The blower is de-
energized after the fan off delay for heating has elapsed. The
draft motor performs a 30-second post purge.
IGNITION CONTROL BOARD
FIRST STAGE OF HEATING
When the ICB receives a call for first stage of heating, “W1,”
the draft motor is energized. Once the draft motor has been
proven, a 30-second purge is initiated. At the end of the
purge, both main valves of the GV are opened, and the spark
ignitor is energized for 10 seconds. The ICB then checks for
the presence of flame. If flame is detected, the ICB enters a
flame stabilization period. If flame was not detected, both
main valves close, and a retry operation begins.
TABLE 23: ELECTRIC HEAT LIMIT SETTING
UNIT (TONS)
VOLTAGE
HEATER
kW
LIMIT
SWITCH
OPENS °F
12.5
208/230
18
150
12.5
24
150
12.5
34
150
12.5
54
150
12.5
480
18
150
12.5
24
150
12.5
34
150
12.5
54
150
12.5
600
18
150
12.5
24
150
12.5
34
150
12.5
54
150
TABLE 24: ELECTRIC HEAT ANTICIPATOR
SETPOINTS
SETTING (AMPS)
W1
W2
0.13
0.1
