Mitsubishi Electric PURY-80TMU Service Handbook page 37

(5) Oil return control (Electronic expansion valve <SLEV>)
• Oil return LEV (SLEV) opening is dependent on compressor frequency and ambient temperature.
• SLEV is closed (0) when compressor stops, and SLEV is set (64) for 10 minutes after starting compressor.
(6) Defrost operation control
1) Starting of defrost operations
• After integrated 50 minutes of compressor operations, defrosting operations start when –6˚C (21˚F) 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 (46˚F) or more.
(Defrosting operations do not stop for 4 minutes after starting, except when piping temperature exceeds (TH5 and
TH7) 20˚C (68˚F) and 0.98MPa (142psi).
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.
(7) 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.
(8) Control of outdoor unit fan and outdoor unit heat exchanger capacity
1) Control system
Depending on capacity required, control outdoor fan flow rate with phase control, for maintaining evaporation
temperature (0˚C (32˚F)) in cooling operations, and high pressure saturated temperature (49˚C (120˚F)) in heating
operations.
2) Control
• Outdoor unit fan stops when compressor stops.
• Fan is in full operation for 5 seconds after starting.
• Outdoor unit fan stops during defrosting operations.
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