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Defrost Operation Control - Mitsubishi Electric PURY-HP72 Service Handbook

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[5-2 Outdoor Unit Control ]

Defrost Operation Control

(1) Starting the defrost operation
The defrost cycle will start when all of the three conditions (outside temperature, cumulative compressor operation time, and
pipe temperature) under <Condition 1>, <Condition 2>, or <Condition 3> are met.
Outside temperature
Cumulative compressor
operation time
Pipe temperature
1) Pipe temperature(TH6)
SW4 (915) OFF
-10ºC [14ºF]
SW4 (915) ON
The defrost cycle will not start if other outdoor units are in the defrost cycle or until a minimum of 10 minutes have passed
since the completion of the last defrost cycle.
If 10 minutes have passed since compressor startup or since the completion of a defrost cycle, a forced defrost cycle can be
started by setting DIP SW4 (913) to ON.
Even if the defrost-prohibit timer is set to 90 minutes (or 150 minutes for "Condition 3" to be met), the actual defrost-prohibit
time for the next defrost cycle is 50 minutes if the last defrost cycle took 12 minutes.
All units in the heating mode will simultaneously go into the defrost cycle in a system with multiple units. The units that are
not in operation may or may not go into the defrost cycle, depending on the cumulative operation time of their compressors.
Condition 1
-5ºC [23ºF] or
50 minutes or more
90 minutes or more if the defrost prohibit timer is set to 90.
The pipe tempera-
The pipe temperature has stayed below the
ture has stayed be-
value obtained from the formula "Outside
low the
temperature (TH7) - 5ºC [23ºF] " for three
temperatures in the
minutes, or the 63LS reading has stayed
table below (Note1)
below the value obtained from the formula
for three minutes.
"1.5 + 0.02 × (20+TH7ºC) (kgf/cm
[21.3+0.158×(4+TH7ºF) (lb/in
-8ºC [18ºF]
-5ºC [23ºF]
-5ºC [23ºF]
Condition 2
-5ºC [23ºF] or below
) ] " for three
- 127 -
Condition 3
250 minutes or more
The pipe temperature has
stayed below the temperatures
in the table below (Note1) for
three minutes

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