Mitsubishi Electric CITY MULTI PUHY-P108 Service Handbook page 161

[ VII Control ]
-7- Defrost Operation Control <PUHY>
(1) Starting the defrost operation
Defrost operation is started when the pipe temperature (TH5) of -10°C [14°F] or below (-8°C [18°F] or below for P126-
type and above) has continuously been detected for 3 minutes after the integrated compressor operation time of 50 min-
utes have passed (90 minutes when the defrost prohibit timer is set to 90 minutes).
If 10 minutes have passed since compressor start-up or since the completion of defrost operation, forced defrost opera-
tion 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.
(2) Defrost operation
Compressor frequency
Outdoor unit fan
SV1
SV3
(P168-P234 models only)
21S4a
21S4b
(P144-P234 models only)
SV5b
(P144-P234 models only)
LEV1
(3) Stopping the defrost operation
Defrost operation will stop when 12 minutes have passed since the beginning of defrost operation (15 minutes when the
defrost prohibit timer is set to 90 minutes), or when the piping temperature (TH5) of 10°C [50°F] or above has been con-
tinuously detected for 2 minutes (TH5 above 7°C [45°F] for 2 minutes for P126 model and above).
Defrost operation will not stop its operation for 2 minutes once started unless the piping temperature exceeds 25°C [77°F]
within 2 minutes, in which case the operation will stop (Above 20°C [68°F] within 2 minutes for P126 model and above).
(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.
Model No.1 Compressor
P72 model
P96 model
P108 model
P126 model
P144 model
P168 model
(50/60 Hz)
P192 model
(50/60 Hz)
P204 model
(50/60 Hz)
P216 model
(50/60 Hz)
P234 model
(50/60 Hz)
480 pulses
- 152 -
No.2 Compressor
52
53
65
114
114
70/60 ON (50/60 Hz)
70/60 ON (50/60 Hz)
110/100 ON (50/60 Hz)
110/100 ON (50/60 Hz)
110/100 ON (50/60 Hz)
Stopped
ON
ON
OFF
OFF
OFF
-
-
-
-
-