66354-BIM-D-0904
54
Unitary Products Group
This limit is monitored regardless of unit operation sta-
tus, 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 26).
SAFTEY CONTROLS
The unit control board monitors the temperature limit
switch of electric heat units.
The control circuit includes the following safety con-
trols:
1.
Temperature Limit Switch (TLS 1, 2).
This control is located inside the heater compart-
ment and is set to open at the temperature indi-
cated in the Limit Control Setting Table 21. 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 compart-
ment and is set to open at the temperature indi-
cated in the Limit Control Setting Table 21. 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 26.
RESET
Remove the call for heating by lowering the thermostat
setting lower than the conditioned space temperature.
This resets any flash codes.
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 low-
ering of the temperature within the conditioned space.
Refer to Table 22 for the required heat anticipator set-
ting.
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 cen-
trifugal switch contact, located on the end of the draft
TABLE 21: LIMIT CONTROL SETTING
18
36
54
72
18
36
54
72
18
36
54
72
18
36
54
72
TEMPERATURE LIMIT
SWITCH 1, 2
OPENS,
0
F
TEMPERATURE LIMIT
SWITCH 3, 4, 5, 6
OPENS,
0
F
UNIT
(Tons)
VOLTAGE
HEATER
kW
120
170
120
170
120
170
120
170
140
200
140
200
140
200
140
200
120
120
120
120
120
120
120
120
170
170
170
170
~
~
~
~
15
17.5, 20,
25
15,17.5,
20, 25
240
240
460
600
15,17.5,
20, 25
TABLE 22: ELECTRIC HEAT ANTICIPATOR
SETPOINTS
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
