175615-YIM-A-0306
Unitary Products Group
37
ELECTRIC HEATING SEQUENCE OF OPERATIONS
The following sequence describes the operation of the
electric heat section.
Single-stage heating (applies only to 5, 7 & 10 kW
230V heaters and to 7, 10, & 15 kW 460V and 575V
heaters. All other heaters MUST use a two-stage ther-
mostat):
a. Upon a call for heat by the thermostat, the heater
sequencer (1S) 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.
Two-stage heating (applies only to 15, 20 and 30 kW
230V heaters and 20 and 30 kW heater 460V and
575V heaters.):
a. Upon a call for first-stage heat by the thermostat, the
heater sequencer (1S) (15, 20, 30 kW 230 volt) and
contactor (2M) (20, 30 kW 460 and 575 volt) 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
sequencer (2S) (12, 20, 30 kW 230 volt) or
contactor (3M) (20, 30 kW 460 and 575 volt)
will be energized. After completing the speci-
fied fan on delay for heating, the UCB will ener-
gize the blower motor.
b. The thermostat will cycle the electric heat to satisfy
the heating requirements of the conditioned space.
SAFETY CONTROLS
The control circuit includes the following safety controls:
1. Temperature Limit Switch (TLS) - This control is
located inside the heater compartment and is set to
open at the temperature indicated in the Electric
Heat Limit Control Setting Table 28. It resets auto-
matically. The limit switch operates when a high
temperature condition, caused by inadequate sup-
ply air flow occurs, thus shutting down the heater
and energizing the blower.
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 lowering of
the temperature within the conditioned space. Refer to
Table 29 for the required heat anticipator setting.
TABLE 28: ELECTRIC HEAT LIMIT CONTROL
SETTING
VOLTAGE
kW
TEMPERATURE LIMIT SWITCH Open Temp
º
F
5
1
140
7
1,3
140
10
1,2,3
140
15
2,4,6
140
1,2,3,4,5
140
6
150
30
1,2,3,4,5,6
150
5
1,2,3
140
7
1,2,3
140
10
1,2,3
150
15
2,4,6
140
20
1,2,3,4,5,6
150
1,3,5
160
2,4,6
150
7
2,4,6
140
10
2,4,6
140
15
2,4,6
140
20
3
160
30
3
150
10
2,4,6
140
15
2,4,6
140
20
5
160
30
5
150
20
30
230-3-60
460-3-60
575-3-60
230-1-60
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