Defrost Operation Control - Mitsubishi Electric PUHY-HP72 Service Handbook

[5-2 Outdoor Unit Control ]
5-2-7

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
(TH7)
Cumulative compressor
operation time
Evaporating tempera-
ture (Te)
1) Evaporating temperature (Te)
SW4 (915) OFF
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, 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.
HWE18240_GB
Condition 1
-5ºC [23ºF] or above
50 minutes or more
90 minutes or more if the defrost prohibit timer is set to 90.
The evaporating temperature
has stayed below the tempera-
ture in the table below (Note1)
for 3 minutes
HP72 - 120
-11 ºC
-8 ºC
Condition 2
-5ºC [23ºF] or below
(Te 1.1 × TH7 - 7.5) continued
for 3 minutes or [{1.5 + 0.02 x
(20+TH7)} > 63LS] continued
for 3 minutes
Condition 3
250 minutes or more
The evaporating temperature
has stayed below the tempera-
ture in the table below (Note1)
for 3 minutes
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