
– 21 –
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. Condenser fan speed is controlled by the same method (Pulse Width Modulation) used to
control evaporator fan speed. The condenser fan and evaporator fan will usually operate at the same
speed. No rpm/feedback wire is used for the condenser fan.
Fresh Food Fan
A variable speed fresh food fan is located in the top of the fresh food section. When activated, the fresh
food fan will draw cool air from the freezer compartment into the fresh food compartment, providing
cooling independent of evaporator fan operation.
The main control board gathers information from the fresh food thermistors to determine when, and at
what speed, fan operation should occur. A constant 12 VDC is provided to the fan from the main control
board and switching occurs on the neutral side. Speed is regulated by Pulse Width Modulation on the
common side of the fan. When operating, the common side of the circuit is pulsed open and closed.
This pulsing 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 12 VDC pulse.
High Speed (10.5 VDC measured)
Medium Speed (7.5 VDC measured)
Low Speed (5.5 VDC measured)
10.5 VDC
7.5 VDC
5.5 VDC
12 VDC
0 VDC
0 VDC
0 VDC
12 VDC
12 VDC
High Speed (12 VDC measured)
Medium Speed (10 VDC measured)
Low Speed (9 VDC measured)
12 VDC
10 VDC
9 VDC
12 VDC
0 VDC
0 VDC
0 VDC
12 VDC
12 VDC
Содержание PSH23SGNAFBS Series
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