Mitsubishi Electric SLH Series Technical & Service Manual page 53

(6) Defrosting
Defrosting of outdoor heat exchanger is controlled by dicer P.C. board, with detection by the defrost thermistor RT61.
1Defrost starting conditions
When all conditions of a),b) are satisfied, the defrosting operation starts.
a) Under the heat operation, the compressor cumulative operation time exceeds 40 minutes without the defrosting opera-
tion working.
b) The defrost thermistor RT61 reads - 3°C or less.
2Defrost terminating conditions
When the condition d) or e) is satisfied, the defrosting operation stops.
d) The defrost thermistor RT61 reads 3.1°C or more.
e) The defrosting time exceeds 10 minutes.
<Defrosting time chart>
Defrost thermistor
RT61
3.1: or more
-3: or less
Outdoor 52C relay
ON
(Compressor)
OFF
ON
X62
(Reversing valve)
OFF
SR61 ON
Outdoor fan
OFF
ON
Defrost
counter
OFF
ON
Indoor fan
OFF
NOTE w When the indoor coil thermistor reads above 18°C, indoor fan operates at VLo for 30 seconds.
w When the indoor coil thermistor reads 18°C or less, the indoor fan stops.
15 sec.
30 sec.
Max 10 min.
VLo
w
53
30 sec.
15 sec.