3
Operating Options
The furnace is shipped from the factory in a “Standard Heating Mode” (all switches are in the Down position). When the thermostat calls for heat, the
automatic controls will be activated and the furnace turned “ON”.
The blower will run at low speed or higher speed (as selected by
SPEED SELECTOR
switch).
As the furnace heats up, it automatically switches to the pre-programmed heating speed when additional elements are activated by the electronic
control, if it was initially set to run at low speed. The timing of this blower speed change will depend on whether F
AST
or S
LOW
is selected on the
HEAT
ACTIVATION
switch.
You may, however, change from the Standard Heating Mode by using the controls built into your furnace.
The
SPEED SELECTOR
switch is used to control the fan speed
(ventilation). Even if there is no call for heat, the ventilation can be
controlled by the thermostat; the fan speed is determined by this switch.
H
IGH
– The blower motor will operate at low speed.
L
OW
– The blower motor will operate at a higher speed.
During spring or fall, you may require less rapid response when the
thermostat calls for heat.
S
LOW
– The elements take more time to be activated.
F
AST
– The elements are activated faster.
4
Breakers
D Series furnaces are equipped with breakers, located on the
front panel of the unit.
These devices protect the heating
elements from overcurrent. If this situation occurs, the breakers
will open to cut the power from the heating elements only.
NOTE: The number of breakers varies according to the furnace
model; 21D10 model has no breakers, 21D15, 21D18 and
21D20 models have 2 breakers, and 21D23 and 21D25 models
have 3 breakers. Refer to Section 8 Wiring Diagrams.
WARNING
Breakers do not cut power to entire furnace, only to the heating elements. Do not use the breakers to turn off the furnace. The
power to the whole unit can only be cut from the main electrical panel.
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