Warm Air Control; Flow Soft Control; High Pressure Protection - Mitsubishi Electric MSH09TW Service Manual

<MSH12/15/17>
When the compressor is operating,
(1) if the temperature of indoor coil thermistor RT12 is less than 64°F or, the indoor fan operates at Very Low.
But if the temperature of room temperature thermistor RT11 is 59°F or less, the fan stops.
(2) if the temperature of indoor coil thermistor RT12 is more than 72°F, the indoor fan operates at set speed.
Indoor coil thermistor
RT12 temperature
NOTE : If the temperature of RT12 reads from 64°F to 72°F at the air conditioner starting and also after defrosting,
this control works.

(3) Warm air control.

When any condition of 1(a. ~ d.) and the condition of 2 as follows are satisfied at the same time, warm air control
works.
1 a.) when the operation mode has been changed to HEAT mode
b.) when cold air prevention has been released
c.) when defrosting has been finished
d.) when the compressor starts in HEAT mode
2 When the temperature of indoor coil thermistor RT12 is less than 99°F.
When warm air control works, the indoor fan speed changes as follows to blow out warm air gradually.
Gradation of indoor fan speed in initial
The upper limit of the indoor fan speed in MANUAL is the set speed.
The upper limit of the indoor fan speed in AUTO is the speed decided by indoor fan speed control.
When the temperature of RT12 has been 99°F or more, or when the set speed has been changed, this control is
released and the indoor fan speed is the set speed.

(4) Flow soft control

When the thermostat (compressor) is off, the indoor fan operates as follows.
<MSH09> less than 64°F
64°F or more
<MSH12/15/17>
2. High pressure protection (Refer to page 70 for MXZ30TN MXZ30TN2)
During heating operation, the outdoor fan motor is controlled by the indoor coil thermistor RT12 temperature for excess
rise protection of compressor discharge pressure.
Outdoor fan OFF : 126˚F (MSH09),
Outdoor fan ON : 118˚F (MSH09),
High pressure protection time chart
Example
Indoor coil thermistor
RT12 temperature
126˚F(MSH09)
122˚F(MSH12/15/17)
118˚F(MSH09)
115˚F(MSH12/15/17)
Outdoor fan motor
NOTE: During high pressure protection and for 4 minutes and 15 seconds after high pressure protection, defrosting of
outdoor heat exchanger is not detected by the defrost thermistor RT61.
Cold Air Prevention
<Time condition>
less than 2 minutes
2 minutes to 4 minutes
more than 4 minutes
< RT12 > < Indoor fan speed >
off
Very Low
— Very Low
122˚F (MSH12/15/17)
115˚F (MSH12/15/17)
ON
OFF
Released
64°F 72°F
<Indoor fan speed>
Low
Med.
High
NOTE : When the thermostat(compressor) turns on, the indoor
fan operates at set speed. But until cold air prevention
and warm air control is released, the indoor fan follows
them.

High pressure protection

Released
ON
OFF
58
Indoor fan speed
Set speed
Very Low or stop
Outdoor fan
126˚F
118˚F (MSH09)
(MSH09)
122˚F
115˚F (MSH12/15/17)
(MSH12/15/17)
Outdoor fan motor
turn OFF
Outdoor fan motor
turn ON
OFF
ON