Defrost Operation; Defrost Start; Defrost-Start Conditions; Defrost End - Mitsubishi Electric CAHV-P500YA-HPB Service Handbook

[ 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 3 is met.
Defrost operation will be performed individually in the circuit that meets the defrost-start condition below. Defrost operations
will not be performed simultaneously in multiple circuits.

Defrost-start conditions 1

1) Three minutes have passed since the compressor started
up.
2) Forty-five minutes have passed since the unit received an
operation command signal.
3) Cumulative compressor operation time after the completion
of the last defrost cycle has reached 45 minutes.
4) The air-side heat exchanger inlet temperature is equal to or
below the defrost-start temperature. (See the figure at right.)
5) Inlet water temperature is above 18ºC.
6) No other circuits are in the defrost cycle.
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 inlet temperature is below -31ºC.
4) Inlet water temperature is above 18ºC.
Defrost-start conditions 3
1) Three minutes have passed since the compressor started up.
2) Forty-five minutes have passed since the unit received an operation command signal.
3) Cumulative compressor operation time after the completion of the last defrost cycle has reached 240 minutes.
4) Air-side heat exchanger inlet temperature is equal to or below 0 ºC.
5) Inlet water temperature is above 18 ºC.
6) No other circuits are in the defrost cycle.

2. Defrost end

The defrost cycle will end when one of the following conditions is
met.
Whether the defrost-end condition is met is determined individu-
ally for each circuit.
1) An air-side heat exchanger inlet temperature of 15ºC or
above has been detected for 120 seconds.
2) An air-side heat exchanger inlet temperature of 25ºC or
above was detected.
3) Ten seconds have passed since the beginning of the defrost
cycle or later, the high-pressure has reached 3.0 MPa or
above.
4) The inlet or outlet water temperature has dropped below the
value obtained by the following formula: Compressor fre-
quency during operation × 0.5 - 22 (ºC).
5) Twelve minutes have passed since the beginning of the de-
frost start (20 minutes, if the defrost operation is performed
at the defrost-start setting 2).
6) When the operation command signal is off.
HWE10060
0
-5
-10
-15
-20
-25
-30
-20 -15
30
25
20
15
10
60 65
- 81 -
-10 -5 0 5
Outside temp. (°CDB)
70 75 80 85 90
Compressor frequency (Hz)
10 15
95 100
GB