Defrost Operation - Mitsubishi Heavy Industries V Multi FDC71VNX Technical Manual

ii) The outdoor unit heat exchanger temperature is detected always and, when the number of revolutions of the outdoor
fan speed has been increased or decreased, there is no change of fan speed for 20 seconds.
iii) Rage of the outdoor unit fan speed under this control is as follows.
a) Lower limit: 130min
b) Upper limit: 500min
iv) As any of the following conditions is established, this control terminates.
a) When the outdoor air temperature is in the zone
higher is established for 40 seconds or more continuously.
b) When the outdoor fan speed is 500rpm and the outdoor unit heat exchanger temperature at 30°C or higher is
established for 40 seconds or more continuously.
c) When the outdoor unit heat changer temperature at 45°C or higher is established for 40 seconds or more.
(e) Caution at the outdoor unit fan start control (3 phase models only)
When the outdoor unit fan is running at 400min
only, without starting up the outdoor fan. This is normal.
(f) Snow protection fan control
If the dip switch (SW3-2) on the outdoor unit control PCB is turned ON, the outdoor unit fan is operated for 30 seconds
at 4 tap speed once in every 10 minutes depending on the outdoor air temperature (detected with Tho-A) in the stop
mode or anomalous stop mode.

(5) Defrost operation

(a) Starting conditions
If all of the following defrost operation conditions A or
conditions B are satisfied, the defrost operation starts.
i) Defrost conditions A
a) Cumulative compressor operation time after the
end of defrost operation has elapsed 37 minutes,
and the cumulative compressor operation time
after the start of heating operation (remote control
ON) has elapsed 30 minutes.
b) After 5 minutes from the compressor ON
c) After 5 minutes from the start of outdoor unit fan
d) After satisfying all above conditions, if temperatures
of the outdoor unit heat exchanger temperature
thermistor (Tho-R1, R2) and the outdoor air
temperature thermistor (Tho-A) become lower
than the defrost operation start temperature
as shown by the right figure for 15 seconds
continuously.
ii) Defrost conditions B
a) When previous defrost ending condition is the time out of defrost operation and it is in the heating operation
after the cumulative compressor operation time after the end of defrost operation has become 30 minutes.
b) After 5 minutes from the start of compressor
c) After 5 minutes from the start of outdoor unit fan
(b) Ending conditions
When any of the following conditions is satisfied, the heating operation starts.
i) When it has elapsed 8 minutes and 20 seconds after the start of defrost operation.
ii) When the outdoor unit heat exchanger temperatures (Tho-R1, R2), whichever the lower, becomes 7°C or higher
for 10 seconds continuously.
-1
-1
-1
before operating the compressor, it may operate with the compressor
Snow protection fan
control ON
3
Outdoor air temperature (°C)
328
-
and the outdoor unit heat exchanger temperature at 30°C or
Snow protection fan
control OFF
5
Model 71 ~ 250
-2
-5
-6
-10
-15
-20
-25
-27
-30
-25 -20 -15
-18
Outdoor air temperature (℃)［Tho-A］
Model 71
-8
-10
-15
-20
-24
-25
-30
-31
-35
-25 -20 -18 -15
Outdoor air temp. (℃)［Tho-A］
Model 100 ~ 250
-8
-10
-
-15
-20
'19 • PAC-T-327
Defrost operation start
temperature zone
-10 -5 0 5 6
Defrost operation start
temperature zone
-10 -5 0 5 6
Defrost operation start
10
10