Mitsubishi Electric PUHY-200YMF-B Service Handbook page 66

2 PURY-(P)200·250YMF-B
1) Starting of defrost operations
• After integrated 50 minutes of compressor operations, defrosting operations start when –8˚C : P-YMF-B, –6˚C :
YMF-B or less of piping temperature (TH7) is detected for 3 consecutive minutes.
• Forcible defrosting operations start by turning on forcible defrost switch (SW2-7) if 3 minutes have already elapsed
after compressor start or completion of defrosting operations.
2) Completion of defrosting operations
Defrosting operations stop when 10 minutes have passed since start of defrosting operation, or piping temperature
(TH5) reaches 8˚C or more.
(Defrosting operations do not stop for 4 minutes after starting, except when piping temperature exceeds (TH5 and
TH7) 20˚C and Pd >10kg/cm
3) Defrosting prohibition
Defrosting operations do not start during oil recovery, and for 10 minutes after starting compressor.
4) Trouble during defrosting operations
When trouble is detected during defrosting operations, the defrosting operations stop, and defrosting prohibition
time decided by integrated operation time of compressor is set to be 20 minutes.
5) Change in number of operating indoor units during defrosting operations
• In case number of operating indoor units changes during defrosting operations, the defrosting operations continue,
and control of unit number change is performed after the defrosting operations are finished.
• Even in case all indoor units stop or thermostat is turned off during defrosting operations, the defrosting operations
do not stop until expected defrosting activities are completed.
(8) Control of liquid level detecting heater
Detect refrigerant liquid level in accumulator, and heat refrigerant with liquid level heater for judging refrigerant
amount. 6 steps of duty control is applied to liquid level heater depending on frequency and outdoor air temperature,
1minute after starting compressor.
(9) Judgement and control of refrigerant amount
1 PU(H)Y-(P)200·250YMF-B
Judge refrigerant amount by detecting refrigerant liquid surface accumulator.
1) Judgement of accumulator liquid level
Return refrigerant from accumulator liquid level detecting circuit to compressor inlet pipe, detect piping temperature,
and judge liquid level.
When heated with heater, liquid refrigerant temperature is almost equal to low pressure saturation temperature, and
gas refrigerant temperature is a little higher than low pressure saturation temperature. By comparing these tempera-
tures with Te (low pressure saturation temperature) : P-YMF-B, TH2 : YMF-B in accumulator inlet portion, refrigerant
liquid level can be judged.
Accumulator liquid level is judged in 3 steps as shown in the figure, from Te or TH2 and liquid level detecting tem-
peratures (TH3, TH4). After deciding refrigerant status (Liquid : TH3 and TH4 are Te or TH2 +5˚C or less, Gas : TH3
and TH4 are Te or TH2 +5˚C or more), judge liquid level by comparing TH3 and TH4.
2
G (0.98MPa).)
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