16
Blower Motor Speed Selection
These furnaces are equipped with blowers, which
have multi-speed direct drive motors.
The blower speed selected is dependent upon the
design and static pressure loss of the duct system.
The duct system external static pressure includes
the combined total of the supply and return ducts
and any plenum type air conditioning coil if used.
The furnace must be adjusted to operate at or below
the maximum external static (in. W.C.), and within
the air temperature rise range as shown on the unit
rating plate and in the specification table.
Dependent upon the conditions in a particular
installation, the blower speeds may need to be
changed to give the proper operation on cooling or
heating. The table above shows the proper blower
speed to use for cooling operation.
SHOCK HAZARD – Be sure electrical power to
furnace is turned off before changing motor
speeds.
These leads should be connected in the control box
to either the heating terminal or the cooling terminal,
depending on the airflow desired. The unused motor
speed lead(s) should be connected to the terminals
marked PARK on the blower control board in the
furnace control box.
Motor Terminal Identification
Four-speed motors
White – Common
Black - High
Blue - Medium High
Yellow - Medium Low
Red – Low
Three-speed motors
White - Common
Black - High
Blue – Medium
Red – Low
MOTOR SPEED TAP SELECTION FOR COOLING
COOLING SYSTEM CAPACITY, BTUH
Furnace
Input
Blower
Wheel
18,000
24,000
30,000
36,000
42,000
48,000
60,000
50,000
10 x 8
Low
Med.
High
75,000
10 x 8
Low
Med.
High
75,000
10 x 10
Low
Med. Low
Med. High
High
100,000
10 x 10
Low
Med. Low
Med. High
High
100,000
(2) 10 x 6
Low
Med. Low
Med. High
High
125,000
(2) 10 x 6
Low
Med. Low
Med. High
High
Blower Timings
The electronic furnace control supplied on this
furnace controls the blower delay timings.
The heating on delay, from when the gas valve
opens to when the circulating blower comes on, is
fixed at 30 seconds and is not adjustable.
The heating off delay, from when the gas valve
closes, to when the circulating blower shuts off, is
factory set at 180 seconds. This timing may be
adjusted to 60, 90, 120 or 180 seconds on the
electronic furnace control. The furnace control has
four pins and a small jumper plug, which is used to
adjust the blower off delay. See Figure 11.
FIGURE 11 – BLOWER TIMING CHANGE