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speed and medium-speed operation. When operating in low and medium speeds, voltage is sent in
pulses (much like a duty cycle) as opposed to an uninterrupted flow. This pulsing of 12.6 VDC produces
effective voltage being received at the motor, which is the equivalent to a reduction in voltage. Fan speed
will be selected and maintained by the control board regulating the length and frequency of the 12.6 VDC
pulse.
One complete revolution of the motor is comprised of all 4 poles. To determine the rpm of the fan:
Measure the frequency being applied to the motor. Multiply this number by 15 (60 seconds divided by 4
poles). For example, a frequency measurement of 200 Hz multiplied by 15 would show a fan speed of
3000 rpm (15 x 200 = 3000). Temperature may cause some fan speed variation. Fan speed may vary
+/- 5%, depending on the temperature, with higher temperatures causing slightly higher speeds.
The evaporator fan motor uses a 4-wire connection, utilizing a common wire (white), feedback/rpm
wire (blue), supply wire (red), and a signal wire (yellow).
High Speed (12 VDC measured)
Medium Speed (8 VDC measured)
Low Speed (4 VDC measured)
EVAPORATOR FAN SPEEDS
12 VDC
8 VDC
4 VDC
12 VDC
0 VDC
0 VDC
0 VDC
12VDC
12 VDC
GEA01139
High Speed (12 VDC measured)
Medium and Low Speed (8 VDC measured)