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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 19. 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 19. 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.
Table 19: Limit Control Setting
Unit
Heater
Voltage
(Tons)
Kw
18
36
15
240
54
72
18
17.5, 20
36
240
and 25
54
72
18
36
15, 17.5,
460
20 and 25
54
72
18
36
15, 17.5,
600
20 and 25
54
72
Flash Codes
The UCB will initiate a flash code associated with errors within
the system. Refer to UNIT CONTROL BOARD FLASH CODES
Table 24.
Reset
Remove the call for heating by lowering the thermostat setting
lower than the conditioned space temperature.This resets any
flash codes.
44
Temperature,
Temperature,
Limit Switch
Limit Switch
1, 2
3, 4, 5, 6
°
°
Opens,
F
Opens,
F
120
170
120
170
120
170
120
170
140
200
140
200
140
200
140
200
120
170
120
170
120
170
120
170
120
-
120
-
120
-
120
-
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 20 for the required electric
heat anticipator setting.
Table 20: Electric Heat Anticipator Setpoint
Heater
Voltage
Kw
18
36
208/230-3-60
54
72
18
36
460-3-60
54
72
18
36
575-3-60
54
72
Gas Heating Sequence Of Operations
The following sequence describes the operation of the gas heat
section.
When the thermostat calls for the first stage of heating, the low-
voltage control circuit from "R" to "W1" and "G" is completed,
thru the UCB. The heat relay "RW1" is energized. The "RW1-2"
contacts close energizing the draft motor control. The draft
motor control contacts close and start the draft motor. As the
speed of the draft motor reaches approximately 2500 RPM, the
centrifugal switch contact, located on the end of the draft motor
shaft, closes to power the first stage ignition module "IC1", thru
the "RW1-1" contacts.
Ignition module "IC1" will immediately start the first stage igniter
sparking and will open the redundant valve located inside the
first stage main gas valve "GV1" to allow a flow of gas to only
the first stage carryover tube. Only after the pilot flame has
been ignited and the presence of pilot flame detected at the
"IC1" by a signal sent back through the flame sensor is sparking
terminated and the first stage main gas valve opened.
Gas flows into each of the main burners and is ignited from the
carryover tube flame.
After completing the specified fan on delay for heating, the UCB
will energize the blower motor.
If "IC1" fails to detect a pilot flame, it will continue to try for a
maximum of 85 seconds to ignite the pilot tube. If the pilot flame
is not detected, then "IC1" will lock out first stage furnace
operation for five minutes or until 24V power is removed from
the module either at the unit or by resetting the room
thermostat.
178113-BIM-D-0906
Setting, Amps
Th1
Th2
0.29
-
0.29
0.29
0.29
0.58
0.29
0.58
0.29
-
0.29
0.29
0.29
0.29
0.29
0.29
0.29
-
0.29
0.29
0.29
0.29
0.29
0.29
Unitary Products Group
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