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5803642-TIM-B-0620
specified fan on delay for heating, 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.
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 Tables 24. 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.
46
Table 24: Electric Heat Limit Setting
UNIT (TONS)
ZWTA3 (3)
ZWTA4 (4)
ZWTA5 (5)
ZWTA3 (3)
ZWTA4 (4)
ZWTA5 (5)
ZWTA3 (3)
ZWTA4 (4)
ZWTA5 (5)
Reset
Remove the call for heating by lowering the thermostat setting
lower than the conditioned space temperature.
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 25 for the required electric
heat anticipator setting.
Table 25: Electric Heat Anticipator Setpoints
SETTING, AMPS
W1
0.13
LIMIT
HEATER
VOLTAGE
SWITCH
kW
OPENS °F
3
6
208/230
9
15
6
9
208/230
15
20
6
9
208/230
15
20
24
3
6
480
9
15
6
9
480
15
20
6
9
480
15
20
24
9
600
15
9
600
15
20
9
15
600
20
24
W2
0.1
Johnson Controls Ducted Systems
155
155
170
170
155
170
170
170
155
170
170
170
170
155
155
170
170
155
170
170
170
155
170
170
170
170
170
170
170
170
170
170
170
170
170
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