349218-JIM-F-0512
Johnson Controls Unitary Products
49
on the 72 KW, 240V heater, heater contactors (8M & 9M)
will be energized. After completing the 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.
NOTE:
All 240 & 480V heaters are provided with manual reset
backup protection limits. These will de-energize the
heaters should the primary limit fail to open or the
contactors fail to open in a failure mode.
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 initiated
(See Table 25).
Safety Controls
The UCB monitors the temperature limit switch of electric heat
units.
The control circuit includes the following safety controls:
Temperature Limit Switch (TLs)
1.
Temperature Limit Switch (TLS 1, 2).
This control is located inside the heater compartment and
is set to open at the temperature indicated in the Limit
Control Setting Table 20. 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.
2.
Temperature Limit Switch (TLS 3, 4, 5 and 6).
This control is located inside the heater compartment and
is set to open at the temperature indicated in the Limit
Control Setting Table 20. It is a manual reset limit. These
limit switches will de-energize the heaters should the
primary limit fail to open or the contactors fail to open in a
failure mode.
Flash Codes
The UCB will initiate a flash code associated with errors within
the system. Refer to UNIT CONTROL BOARD FLASH CODES
Table 25.
Reset
Remove the call for heating by lowering the thermostat setting
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 21 for the required electric
heat anticipator setting.
Gas Heating Sequence Of Operations
The following sequence describes the operation of the gas heat
section.
Table 20: Limit Control Setting
Unit
(Tons)
Voltage
Heater
Kw
Temperature,
Limit Switch
1, 2
Opens,
°
F
Temperature,
Limit Switch
3, 4, 5, 6
Opens,
°
F
15
240
18
120
170
36
120
170
54
120
170
72
120
170
17.5, 20
and 25
240
18
140
200
36
140
200
54
140
200
72
140
200
15, 17.5,
20 and 25
460
18
120
170
36
120
170
54
120
170
72
120
170
15, 17.5,
20 and 25
600
18
120
-
36
120
-
54
120
-
72
120
-
Table 21: Electric Heat Anticipator Setpoint
Heater
Kw
Voltage
Setting, Amps
Th1
Th2
18
208/230-3-60
0.29
-
36
0.29
0.29
54
0.29
0.58
72
0.29
0.58
18
460-3-60
0.29
-
36
0.29
0.29
54
0.29
0.29
72
0.29
0.29
18
575-3-60
0.29
-
36
0.29
0.29
54
0.29
0.29
72
0.29
0.29
Table 20: Limit Control Setting
Unit
(Tons)
Voltage
Heater
Kw
Temperature,
Limit Switch
1, 2
Opens,
°
F
Temperature,
Limit Switch
3, 4, 5, 6
Opens,
°
F
