Fujitsu ASU18RLF Service Instructions Manual page 30

3. Defrost Flow Chart
The defrosting shall proceed by the integrating operation time, outdoor temperature
and outdoor heat exchanger temperature as follows.
Ta > 14°F(-10°C)
4°F(-20°C) < Ta < 14°F(-10°C)
=
Tn < 1.4°F(-17°C)
=
Tn < 0.8 × Ta - 11.6
=
Tn < -18.4°F(-28°C)
=
Tn : Outdoor heat exchanger temp.
Ta : Outside air temp.
: Before 5 minutes detected Tn
Tn-1
: Number of operation indoor units
Sn
: Before 5 minutes detected Sn
Sn-1
Heating operation start : Compressor ON
Normal defrost
Ta < 4°F(-20°C)
=
Tn < 0.8 × Ta - 11.6
=
or or
Tn < -18.4°F(-28°C)
=
Defrost Indicator:
[Operation lamp]
7 sec ON / 2 sec OFF
Outdoor HEX temp. : Over 59°F(15°C)
Compressor ON time : Maximum 15 minutes
Integrating defrost
Tn < 21.2°F(-6°C) More than 210 minutes
=
( For continuous operation )
Tn < 26.6°F(-3°C)
(and after 30 minutes,
Tn - Tn-1 < 28.4°F(-2°C)
if the Tn < 26.6°F(-3°C)
and Sn = Sn-1
Tn < 23°F(-5°C)
(and after 3 minutes,
if the Tn < 23°F(-5°C)
Defrost start
3 sec later Compressor : OFF
3 sec later Outdoor fan motor : OFF
35sec later 4WAY valve : OFF
41sec later Compressor : ON
or
Defrost end
01-27
Integrating defrost
(Integrating OFF count defrost)
Compressor OFF count :
40 times
(Less than 10 minutes)
or