Panasonic Urban Multi MX1R Series Service Manual page 447

Outline of Control
3.1.3 Defrost Control
Activates the defrosting operation to melt frost accumulated on the outdoor heat exchanger during heating
operation.
[Defrost start conditions]
When the following conditions are met during heating operation, the defrosting operation is activated.
OR
Tb : Distributor pipe temperature (°C) at heat exchanger outlet (in cooling operation)
Ta : Outside temperature (°C)
Defrost setting
No-setting (Factory set)
When the above conditions are met, the following "defrosting operation preparation" operation is conducted
for 2 minutes, then the defrosting operation is activated.
1. Outputs "oil return, defrost preparation" signal to indoor units.
2. Turns on the liquid injection solenoid valve (SVT) based on Td or DSH.
Td : Discharge pipe temperature
DSH : Discharge super heat temp.
∗ Liquid injection : Refer to page 440.
426
When cumulative compressor operating time from power On or completion of previous
defrosting operation exceeds 20 minutes
&
When condition (Tb ≤ B × Ta – A) remains for 5 minutes (–25 ≤ Tb ≤ –10)
(Value of A based on the following table. When Ta ≥ 7, Ta = 7°C is used in calculation)
When forced defrost setting (local setting) is turned on and Tb < 12.5°C
Defrost change setting
L
A=12
M H
Outside air Ta > 0°C
A=14 A=16
Outside air Ta ≤ 0°C
Function UM Combination "MA1R Series" Using R-407C
PACD011001C2
B
0.6
0.8