Mitsubishi Electric CAHV-R450YA-HPB Service Manual page 107

[ VII Control ]
Control at Start-up
-4- Defrost operation
1. Defrost start
The defrost cycle will start when one of the following conditions 1 through 4 is met.
Defrost operation will be performed in the circuit that meets the defrost-start condition below.
Defrost-start conditions 1
1) Three minutes have passed since the compressor started
up.
2) Cumulative compressor operation time after the completion
of the last defrost cycle has reached 45 minutes.
3) The air-side heat exchanger outlet temperature is equal to
or below the defrost-start temperature. (See the figure at
right.)
4) Inlet water temperature is above 18 ºC.
Defrost-start conditions 2
1) Twenty minutes have passed since the unit received an operation command signal.
2) Cumulative compressor operation time after the completion of the last defrost cycle has reached 20 minutes.
3) Air-side heat exchanger outlet temperature is below -22 ºC.
4) Inlet water temperature is above 18 ºC.
5) Outside temperature is -13 ºC or above.
Defrost-start conditions 3
1) Forty-five minutes have passed since the unit received an operation command signal.
2) Cumulative compressor operation time after the completion of the last defrost cycle has reached 240 minutes.
3) Under low pressure drop suppression control.
4) Inlet water temperature is above 18 ºC.
5) Compressor frequency is below a certain value.
Defrost-start conditions 4
1) Compressor shell superheat is below 10K over 30 minutes.
2) Inlet water temperature is above 18 ºC.
2. Defrost end
The defrost cycle will end when one of the following conditions is
met.
1) 30 seconds have passed since the beginning of the defrost
cycle or later, the high-pressure has reached 1.2 MPa or
above.
2) The inlet or outlet water temperature has dropped below the
value. (See the right graph)
3) 15 minutes have passed since the beginning of the defrost
start (20 minutes, if the defrost operation is performed at the
defrost-start setting 2).
4) When the operation command signal is off.
HWE22020
0
-5
-10
-15
-20
-25
-14 -12
16
15
14
13
12
60 65
- 98 -
-10 -8 -6 -4
Outside temp. (°CDB)
70 75 80 85 90
Compressor frequency (Hz)
-2 0
95 100
GB