Warm Air Control; Flow Soft Control; High Pressure Protection; Defrosting - Mitsubishi Electric Mr.Slim MSZ09UN Service Manual

(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.
<MSZ09UN> less than 64°F
64°F or more
<MSZ12UN>

2. High pressure protection

In HEAT mode the indoor coil thermistor RT12 detects the temperature at the indoor heat exchanger and controls the com-
pressor operational frequency to prevent the condensing pressure from increasing excessively.
Temperature of indoor coil thermistor:RT12
approx. 131°F or below
approx. 140°F to 131°F
approx. 167°F to 140°F
approx. 167°F or above
3. Overload starting
When the room temperature thermistor reads 64°F or above, the compressor runs with its maximum frequency regulated for
3 minutes after the start-up.

4. Defrosting

(1) Starting conditions of defrosting
When the following three conditions, a), b), and c), are satisfied, the defrosting starts.
a) The defrost thermistor reads 26.6°F or below.
b) The cumulative operation time of the compressor has reached any of the set values: 35, 32 and 35 or more minutes.
c) More than 1 minute have passed since the start-up of the compressor.
w Set value of compressor operation time(hereinafter referred to as defrost interval)
The first defrost interval is 35 minutes long, and the second 32 minutes long.The third and subsequent intervals are
set to be longer, and less frequent, depending on defrosting time.
The third and subsequent defrost intervals follow any of the three patterns 10 minutes longer, the same, 10 minutes
shorter compared with the previous defrost interval ... with normal 55 minutes, the longest 115 minutes and the short-
est 30 minutes.
(2) Releasing conditions of defrosting
Defrosting is released when any of the following condition is satisfied:
a) The defrost thermistor reads 55°F or above.
b) Defrosting time has exceeded 10 minutes.
c) Some other modes than HEAT mode is set during defrosting.
<Time condition>
less than 2 minutes
2 minutes to 4 minutes
more than 4 minutes
< RT12 > < Indoor fan speed >
off
Very Low
— Very Low
<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.
Operation frequency
lower at the rate of 6Hz/min.
lower at the rate of 30Hz/min.
Compressor is turned off and it is turned on 3 minutes later.
28
normal