Mitsubishi Electric PRH-P8MYA Technical & Service Manual page 45

(2) Compressor, 4-way valve, and crankcase heater control
1) Determines the operation mode and operates the compressor based on the indoor/outdoor communication or M-
NET communication data.
2) Compressor control has a function which prevents the compressor from restarting within 3 minutes.
3) The 4-way valve is always ON during heating (except during defrosting). In other modes, it is OFF. However, when
the operation mode was changed from heating to stop, the 4-way valve is turned off 10 minutes after the compres-
sor was stopped.
4) While the compressor is stopped, the crankcase heater remains ON. (OFF while the compressor is operating.)
5) When the operation mode is changed while the compressor is operating, the compressor stops and 3 minutes later
restarts in the new mode.
(3) Fan control
Controls the fan speed based on the piping temperature (TH1) to perform cooling at low outdoor temperatures and heating
at high outdoor temperatures.
1) Control at cooling
a) When the compressor stops, the fan stops (fan output=0%).
b) When the power is turned on, or when the compressor is restated after it has been stopped for 30 minutes or
longer, the piping temperature ( TH1) determines the fan output.
When TH ≤ 25˚C
When TH < 25˚C
c) When the compressor is restarted within 30 minutes after it has been stopped, the fan step before the compres-
sor was stopped is selected. However, when the fan output was under 30% when the fan was stopped, 30% is
selected.
d) When the mode was changed from heating to cooling, the fan step conforms to item 2.
e) Two minutes after the fan is started, the fan step (number of units) is controlled every 30 seconds based on the
piping temperature (TH1).
f) When TH1 reaches 50˚C or higher, or when the control high pressure switch (63H2) tripped, the fan output
becomes 100%.
g) Fan output while the compressor is operating is within the 20% to 100% range.
• FAN step
The following expression determines the next fan step count nj+1:
nj + 1 = nj + ∆nj
nj control
• If nj + 1 ≥ 100% nj + 1 = 100%
• If nj + 1 ≥ 20%
• If TH1 ≥ 50 °C or 63H2 is "OFF"
FAN ∆nj
Target condensation
temperature 31 °C
20 ≤ nj < 50
50 ≤
Fan output = 100 %
Fan output = 60 %
nj: Current fan step, ∆nj: Displacement step amount
nj + 1 = 20%
t = 49
t > 49 °C
t > 46
5 3
≤
nj 100
10 4
* In the night mode, the maximum value of nj is 80%. (When TH1 < 50˚C)
nj + 1=100%
20 ˚C
Condensation temperature TH1
t = 46 t = 43 t = 40 t = 36
t > 43 t > 40 t > 36 t > 33
2 2 2 2
3 2 2 2
- 42 -
Outputs are all %.
t = 33 t = 29 t = 26 t = 23
t > 29 t > 26 t > 23 t > 20
0 –2 –2 –3
0 –2 –2 –4
t≤ 20 ˚C
–5
–10