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2) PWM (Pulse Width Modulation) valve
PWM valve is the valve to take away the fixed scroll by lifting up through the difference of pressure after the digital
scroll compress being connected to the outlet and inlet of suction. Therefore, the capacity of compressor is controlled
automatically according to the operation status such as loading when the valve is closed or unloading when the valve
is opened. PWM means the control of ON/OFF signal to the valve for loading/unloading.
(4) Refrigerant flow rates control
Refrigerant flow rates through the electronic expansion valve are controlled by the 2 factors which are the
temperature difference between inlet and outlet of evaporator and the difference between room and set temperature.
a. An electronic expansion valve optimally distributes refrigerant flow rates to each room and the fuzzy logic enables
comfortable cooling more precisely; refer to the figure below.
b. The air conditioner senses the temperature difference between inlet and outlet of evaporator, plus the temperature
difference between room and set temperature. And it calculates the superheat and the room temperature status,
then adjusts refrigerant flow rates after deciding the opening steps of valve.
①
Falling room temperature
②
Rising room temperature
③
Open electronic expansion valve
④
Closed electronic expansion valve
1
0.5
0
-0.5
-1
①②
③
④
Relationship between PWM valve and loading/unloading
PWM valve open PWM valve close
Unloading
Period (Cycle Time, T)
Loading
compression
non-compression
(rotating in vain)
DVM E-D/B(chapter1)-E<03759 3/21/02 6:55 PM Page 9