Defrost Operation Control - Mitsubishi Electric R410A 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
Evaporation tempera-
ture (Te)
1) Evaporation 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.
(2) Defrost operation
Compressor frequency
Outdoor unit fan
SV1a
SV5b
21S4a
21S4b, 21S4c
SV9
SV2
LEV1
LEV2a, LEV2b
*1. This value may be greater than 0 pulse depending on the 63LS and TH4 status.
HWE14080
Condition 1
-5ºC [23ºF] or above
50 minutes or more
90 minutes or more if the defrost prohibit timer is set to 90.
The evaporation temperature
has stayed below the tempera-
tures in the table below (Note1)
for three minutes.
P72 P96
-13 ºC -11 ºC
-8 ºC -8 ºC
Model
72 model
96 model
120 model
144 model
168 model
- 97 -
Condition 2
-5ºC [23ºF] or below
"Te Outdoor air temperature
(TH7) x 1.1 - 7.5 ºC" or less
continues for 3 minutes
Or {(1.5+0.02 x (20+TH7) >
63LS) continues for 3 minutes}
P120 P144
-11 ºC -11 ºC
-8 ºC -8 ºC
Compressor frequency
79 Hz
79 Hz
107Hz
107Hz
129Hz
Stopped
ON
OFF(open)
OFF
OFF
OFF
ON
*1
0 pulses
3000 pulses
Condition 3
250 minutes or more
The evaporation temperature
has stayed below the tempera-
tures in the table below (Note1)
for three minutes.
P168
-11 ºC
-8 ºC
GB