Mitsubishi Heavy Industries FDT28KXE6A Service Manual page 18

(8) Defrrosting (Master unit/Slave unit)
If the defrost starting conditions at the outdoor heat exchanger are established, defrost operation starts.
(a) Temperature conditions for defrosting
(i) Conditions for starting defrost
When all of following conditions are satisfied, defrost operation will be started.
1) When the cumulative operation time
of the compressor becomes 33 minutes
after completion of previous defrost
operation, or it becomes 33 minutes after
heating operation starts.
2) When 8 minutes have elapsed after one
compressor is turned ON from the state
of all compressors OFF.
3) When 8 minutes have elapsed after one
outdoor fan is turned ON from the state
of all outdoor fan OFF.
4) After all of the above conditions are satisfied, and
when the temperatures detected with the outdoor heat exchanger temperature thermistor (Tho-R1,-R2) and
outdoor air temperature thermistor (Tho-A) are below the defrost starting temperature mentioned in the above
graph continuously for 3 minutes.
(ii) Conditions for finishing defrost
• Standard (J14 is shorted)
1) When the temperature detected with both outdoor heat exchanger temperature thermistors (Tho-R1 and
Tho-R2) is higher than 9ºC
2) Or when 12 minutes have elapsed since defrosting started.
• Cold region setting (J14 is open)
1) When (Tho-R1 and Tho-R2) > = 9ºC is satisfied, after 2 minutes and 30 seconds have elapsed since defrosting
started, and when either of following conditions is satisfied, the defrosting end operation starts.
a) 2 minutes and 30 seconds have elapsed since the temperature of either Tho-R1 or Tho-R2 was 14ºC or
higher
b) The temperature of either Tho-R1 or Tho-R2 is 30ºC or higher.
c) 14 minutes have elapsed since defrosting started.
2) When (Tho-R1and Tho-R2) < 9ºC is satisfied, after 2 minutes and 30 seconds have elapsed since defrosting
started, and when either of following conditions is satisfied, the defrosting end operation starts.
a) 5 minutes have elapsed since the temperature of either Tho-R1 or Tho-R2 was 14ºC or higher.
b) The temperature of either Tho-R1 or Tho-R2 is 30ºC or higher.
c) 14 minutes have elapsed since defrosting started.
Fig.1
-2
-6
Cold region
-15
-19
-21
-25
-20 -15
Outdoor air temp. (ºC) [Tho-A]
16
- -
Without J15
Cold region
specification
With J15
Standard
(Factory setting)
Defrost start zone
6