Operating Range - McQuay MDS Series Service Manual

1
Digital Scroll Compressor
Digital Scroll Compressor can be easily identified by the presence of PWM valve. On the other hand, Fix Scroll
Compressors do not have any PWM valve for modulation purpose. The combination of Digital and Fix Scroll
Compressor work according to the following principle:
1. Digital Scroll Compressor is the leading compressor which will turn ON first.
2. With assistance of PWM valve, Digital Scroll Compressor will modulate the refrigerant flow according to
the total indoor capacity required.
3. When the total indoor capacity exceeds the maximum capacity of Digital Scroll Compressor, Fix Scroll
Compressor will turn ON.
4. When Fix Scroll Compressor is ON, Digital Scroll Compressor will continue to modulate the refrigerant
flow accordingly.

1.2 Operating Range

MDS unit is tested under standard condition (27° C DB/19° C WB Indoor and 35° C DB/24° C WB Outdoor for
cooling, 20° C DB/15° C WB Indoor and 7° C DB/6° C WB Outdoor for Heating) and should operate within the
range stated in diagram above.
2
PWM
Valve
Total Capacity
Required
° C
Cooling Cycle
50
43° CDB
40
30
20
10
0° CDB
0
-10
-20
Fix Scroll Compressor
16° CWB
-15° CWB
Heating Cycle
Service Manual SM-MDS_(ii)