Midea M-Thermal Series - 5 Protection Control

 M‐ThermalSplit
20190919
Part3‐ Control
Table3‐4.2:Componentcontrolduringcoolingoperation
Component
Wiringdiagram
label
4‐10kW
Controlfunctionsandstates
Invertercompressor 
COMP
●
Controlled according to load requirement from hydronic
system
DCfanmotor FAN
●
Controlled according to outdoor heat exchanger pipe
temperature
Electronicexpansionvalve  EXV
●
Position(steps) from 0(fully closed) to 480(fully open),
controlled according to outdoor ambient temperature,
discharge temperature, suction superheat, compressor
speedandrefrigerantsystempressure
Four‐wayvalve 4‐WAY
●
Off

4.2 CompressorOutputControl
Thecompressorrotationspeediscontrolledaccordingtotheload requirement. Before compressor startup, the
M‐ThermalSplitoutdoorunitdeterminesthecompressortargetspeedaccordingtooutdoorambienttemperature,leaving
watersettemperatureandactualleavingwatertemperatureandthenrunstheappropriatecompressorstartupprogram.
RefertoPart3,3.2“CompressorStartupProgram”.Oncethestartupprogramiscomplete,thecompressorrunsatthe
target rotation speed. During operation the compressor speed iscontrolledaccordingtotherateofchangeinwater
temperature,therefrigerantsystempressureandtherefrigeranttemperature.

4.3 CompressorStepControl
The runningspeedofsix‐pole compressors (usedon4‐10kWmodels) in rotationspersecond(rps)is one third ofthe
frequency(inHz)oftheelectricalinputtothecompressormotor.Thefrequencyoftheelectricalinputtothecompressor
motorscanbealteredatarateof1Hzpersecond.

4.4 Four‐wayValveControl 
Thefour‐wayvalveisusedtochangethedirectionofrefrigerantflowthroughthewatersideheatexchangerinorderto
switch between cooling and heating/DHW operations. Refer to Figures2‐3.1and2‐3.2inPart2,3“RefrigerantFlow
Diagrams”.

Duringheatingand DHWoperations,thefour‐way valveison; duringcoolingand defrostingoperations,the four‐way
valveisoff.

4.5 ElectronicExpansionValveControl
Thepositionoftheelectronicexpansionvalve(EXV)iscontrolledinstepsfrom0(fullyclosed)to480(fullyopen). 
 Atpower‐on:
 TheEXVfirstclosesfully,thenmovestothestandbyposition(480(steps)).Aftercompressorrunsat38Hzfor40
seconds the EXV moves to an initial running position, which is determined according to outdoor ambient
temperature.Afterafurther180seconds,theEXViscontrolledaccordingtosuctionsuperheatanddischarge
temperature.Onceafurther6minuteshaveelapsed,theEXVisthencontrolledaccordingtosuctionsuperheat,
dischargetemperatureandcompressorspeed.
 Whentheoutdoorunitisinstandby:
 TheEXVisatposition480(steps).
 Whentheoutdoorunitstops:
 TheEXV firstmovesto478 (steps)and remainsfor30seconds,then closesfully,then movestothe standby
position(480(steps)).

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