Mitsubishi Electric PUHY-HP144TSHMU-A Service Handbook page 96

[ VII Control ]
-7- Defrost Operation Control
(1) Starting the defrost operation
The defrost cycle starts when outdoor temperature, integrated operation time of compressor, and piping temperature are met
for every range of <condition 1> through <condition 3>.
Outdoor temperature (TH7)
Integrated operation time of
compressor
Piping temperature (TH3)
Defrost cycle does not start while other outdoor units are defrosting or 10 minutes have not passed since resuming operation
after the completion of the defrost cycle.
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 or 150 minutes <condition 3>, the actual defrost-prohibit time for the next
defrost cycle is 50 minutes if the last defrost cycle 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.
(2) Defrost operation
Compressor frequency
Outdoor unit fan
SV1a
SV2
SV6
SV9
21S4a
LEV1
LEV2a , LEV2b
LEV4
(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)
is 10°C[50°F] or above has been continuously detected for 2 minutes.
The defrost cycle does not end for 2 minutes once started unless the pipe temperature exceeds
25°C ( = Outdoor temperature(TH7) - 25)°C
In the multiple-outdoor-unit system, defrosting is stopped on all units at the same time.
(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.
HWE0716A
<condition 1>
- 5°C [23°F] and above
When 50 minutes have passed (90 minutes when the de-
frost-prohibit timer is set to 90 minutes).
At or below -10°C [14°F] for Outdoor temperature (TH7)
3 minutes is at or below -5°C [23°F] for
Or {(1.5+0.02 XTH7>63LS) 3 minutes
for 3 minutes Or {(1.5+0.02 XTH7>63LS)
for 3 minutes.
Model
HP72 model
HP96 model
1400 pulses
5°C [77°F (
- 87 -
<condition 2>
- 5°C [23°F] or below
When 250 minutes have
passed
At or below -10°C [14°F] for
3 minutes
Compressor frequency
60 Hz
60 Hz
Stopped
ON
OFF
OFF
OFF
OFF
200 pulses
460 pulses
= Outdoor temperature(TH7) - 45)°F
<condition 3>
below within 2 minutes.
41°F]
GB