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Mitsubishi Electric PUHY-P72 Service Manual page 108

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[ VII Control ]
-7- Defrost Operation Control
(1) Starting the defrost operation
The defrost cycle starts when the pipe temperature (TH3), in the following table, or below has continuously been detected for
3 minutes after the integrated compressor operation time of 50 minutes have passed.
If 10 minutes have passed since compressor start-up or since the completion of defrost operation, forced defrost operation
will start by turning on the forced defrost switch (DIP SW2-7).
Even if the defrost prohibit timer is set to 90 minutes, the actual defrost prohibit time for the next operation will be 50 minutes
if defrosting took 12 minutes.
In the multiple-outdoor-unit system, all of the outdoor units that are in operation go into the defrost mode simultaneously. The
unit(s) that is stopped at the time defrost operation starts remains stopped.
Model
72 model
96 model
120 model
(2) Defrost operation
Compressor frequency
Outdoor unit fan
SV1a
SV5b, SV5c
21S4a
21S4b, 21S4c
SV9
LEV1
LEV2a
LEV2b
*1. This value may be greater than 0 pulse depending on the 63LS and TH4 status.
(3) Stopping the defrost operation
The defrost cycle ends when 12 minutes have passed since the beginning of the cycle, or when the pipe temperature (TH3)
has been continuously detected for 4 minutes (when SW3-4 is set to OFF) or 2 minutes (when SW3-4 is set to ON) that ex-
ceeds the values in the table below.
The defrost cycle will not end for two minutes once started unless one of the following conditions is met : Pipe temperature
reaches 25°C [77°F] and SW3-4 is set to OFF OR
*1 (5°C [41°F]
25°C [77°F]).
In the multiple-outdoor-unit system, defrosting is stopped on all units at the same time.
Model
72 model
96 model
120 model
(4) Problems during defrost operation
If a problem is detected during defrost operation, the operation will be stopped, and the defrost prohibition time based on the
integrated compressor operation time will be set to 20 minutes.
(5) Change in the number of operating indoor units during defrost operation
Even when there is a change in the number of operating indoor units during defrost operation, the operation will continue, and
an adjustment will be made after the completion of the defrost operation.
Defrost operation will be continued, even if the indoor units stop or under the Thermo-OFF conditions until it has run its course.
HWE0804A
TH3
SW3 - 3 OFF
- 10°C [14°F]
- 10°C [14°F]
- 10°C [14°F]
Model
72 model
96 model
120 model
Stopped
ON
ON
OFF
OFF
OFF
0 pulses
1400 pulses
1400 pulses
=25+TH7°C [77°F+TH7] and SW3-4 is set to ON.
TH3
SW3 - 4 OFF
10°C [50°F]
10°C [50°F]
7°C [45°F]
- 99 -
SW3 - 3 ON
- 5°C [23°F]
- 5°C [23°F]
- 5°C [23°F]
Compressor frequency
65 Hz
65 Hz
103 Hz
*1
SW3 - 4 ON
5°C [41°F]
5°C [41°F]
5°C [41°F]
GB

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