Mitsubishi MSZ-FA-VA Service Technical Manual page 7

3. High pressure protection
In HEAT operation the indoor coil thermistor detects the temperature of the indoor heat exchanger. The compressor opera-
tional frequency is controlled to prevent the condensing pressure from increasing excessively.
4. Overload starting
When the room temperature thermistor RT11 reads 18°C or more, the compressor runs with its maximum frequency regulat-
ed for 10 minutes after the start-up.
5. Defrosting
(1) Starting conditions of defrosting
When the following conditions a) ~ c) are satisfied, the defrosting starts.
a) The defrost thermistor reads -3°C or less.
b) The cumulative operation time of the compressor has reached any of the set valuesw (30, 35, 40, 45, 55, 65, 75, 85,
95, 105, 115, 125, 150 minutes).
c) More than 5 minutes have passed since the start-up of the compressor.
w Set value of compressor operation time(hereinafter referred to as defrost interval)
This is decided by the temperature of defrost thermistor and ambient temperature thermistor, the previous defrosting
time. For example, the first defrost interval is 40 minutes long, and the second is 45 minutes long. The third and sub-
sequent 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 ... 5 or 10 to 20 minutes longer, the same,
or 5 or 10 to 20 minutes shorter compared with the previous defrost interval ... with the longest 150 minutes and the
shortest 30 minutes.
(2) Releasing conditions of defrosting
Defrosting is released when any of the following conditions is satisfied:
a) The defrost thermistor continues to read 5°C or more (MUZ-FA25VA) / 10°C or more (MUZ-FA35VA) for 30 seconds.
b) Defrosting time has exceeded 10 minutes.
c) Any other mode than HEAT mode is set during defrosting.
Time chart of defrosting in HEAT mode (reverse type)
<indoor unit>
Horizontal vane
Indoor fan
<outdoor unit>
Compressor normal
Outdoor fan
R.V. coil
(21S4)
Downloaded from AC-Manual.com Manuals
set position
Very Low (temperature of indoor coil thermistor > 18:)
set speed
30
seconds
OFF
40 30
seconds seconds
5 seconds
ON
ON (HEAT)
horizontal
OFF
Maximum frequency
seconds
OFF
OFF (COOL)
7
set position
set speed
OFF
40 30
seconds
5 seconds
ON
ON (HEAT)