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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 SLOW is selected on the HEAT ACTIVATION switch.
You may, however, change from the Standard Heating Mode by using the controls built into your furnace.
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, 21D25 and 21D27
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.
SLOW
FAST
HEAT ACTIVATION
During spring or fall, you may require less rapid response when the
thermostat calls for heat.
When S
LOW is selected, it takes more time to bring all the elements online.
When FAST is selected, the heating elements come online faster.
Slow (First Stage)
Slow Response Sequence
Fast (Second Stage)
Rapid Response Sequence
Element 1 - Heat on instantly Element 1 - Heat on instantly
Blower on after a 3-second delay Blower on after a 3-second delay
Elements 3 and 5
after a 1-minute delay
Elements 3 and 5
after a 10-second delay
Element 2 after a 2-minute delay Element 2 after a 20-second delay
Element 4 and 6
after a 3-minute delay
Element 4 and 6
after a 30-second delay
NOTE: Elements 4, 5 and 6 only where applicable.
HIGH
LOW
SPEED SELECTOR
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.
LOW – The blower motor will operate at low speed.
HIGH – The blower motor will operate at a higher speed.
FD0003
BREAKERS
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