GE PSH23SGNAFBS Series, Technical Service Manual

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Evaporator Fan
The position of the fan blade in relation to the shroud is important. Refer to illustration for specifications.
5/16" ± 0.03
Blade tip
1.0" ± 0.05 Target
Motor
Air Flow
Orifice
GEA01149
The evaporator fan is the same fan used on previous models; however a significant difference is that the
main control board does not require, nor receive, input from the fan feedback/rpm (blue) wire. The fan
utilizes a permanent magnet, 4-pole, DC motor that operates at three different speeds: high, medium,
and low. The speed of the fan is controlled by the voltage output from the main control board. Voltage
output from the control board to the fan is 13.2 VDC; however to regulate the speed of the fan, the main
control board uses pulse width modulation (PWM). When operating, voltage is sent in pulses (much like
a duty cycle) as opposed to an uninterrupted flow. This pulsing of 13.2 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 main control board regulating the length and frequency of the 13.2 VDC pulse.
One complete revolution of the motor is comprised of all 4 poles. To determine the rpm of the fan, do
the following: 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.
Fans
High Speed (9.5 VDC measured)
Medium Speed (8 VDC measured)
Low Speed (6.5 VDC measured)
9.5 VDC
8 VDC
6.5 VDC
12 VDC
0 VDC
0 VDC
0 VDC
12 VDC
12 VDC