335224-BIM-B-1208
Johnson Controls Unitary Products
55
ELECTRIC HEATING SEQUENCE OF OPERATIONS
The following sequence describes the operation of the elec-
tric heat section.
Two-stage heating:
a.
Upon a call for first stage heat by the thermostat, the
heater relay (RA) will be energized. After completing
the specified fan on delay for heating, the UCB will
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 HEAT 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 41).
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 35. 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 41.
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 36 for the required electric
heat anticipator setting.
TABLE 35: ELECTRIC HEAT LIMIT SETTING
UNIT
VOLTAGE
HEATER
kW
LIMIT SWITCH
OPENS °F
-07
208/230
9
150
-07, -10, -12
18
150
-07, -10, -12
24
150
-07, -10, -12
34
150
-10, -12
54
130
-07
480
9
150
-07, -10, -12
18
150
-07, -10, -12
24
150
-07, -10, -12
34
150
-10, -12
54
130
-07
600
9
150
-07, -10, -12
18
150
-07, -10, -12
24
150
-07, -10, -12
34
150
-10, -12
54
130
