Hitachi RAM-52QH5, Service Manual, Page: 49 / 104

– 60 –
DEFROST
Reversing valve defrost system is employed: it consists of balancing period reversing cycle period balancing period.
When all the following conditions are established defrost is executed:
Normal operation
Defrost start condition (1)
Defrost inhibit period linked to outdoor temperature has passed.
Heat exchange temperature is within defrost range specified by outdoor temperature and heat exchange temperature.
1
3
2
If any one of the following conditions is established, defrost is released:
Defrost release condition (2)
Outputs during defrost (3)
Indoor defrost request: Transmitted to all units being operated in heating mode.
Electric expansion valve
Unit being stopped : [FULL CLOSE] 30 seconds after balancing period has passed [FULL CLOSE] during
reversing cycle period [PCLOSH$] 15 seconds before balancing period is finished
Unit being operated : [DFCTPS] 30 seconds before balancing period is finished Synchronized with step-up
of rotation speed of compressor, opened by [DFSPPS] pulses and reaches MAX opening
degree [DEFSMX] when rotation speed of compressor reaches [DEFMAX].
Compressor : Balancing period for [TDF414] seconds Starting of reversing cycle period by [SDRCT2] min -1 for
Released by condition 1 or 2 during reversing cycle period: [TDF415] Shifted to balancing period.
[TSKTM2] seconds Accelerating by [DFSTEP]min -1 /[TDFSPT] seconds in remaining reversing cycle
period until defrost MAX speed [DEFMAX] is reached Balancing period for [TDF415] seconds
Released by condition 1 during balancing period: When remaining balancing period has elapsed, returned to initial
condition (ASTUS=0).
above graph is showing the ideal value by micon program.
Heat exchange temperature returns (heat exchange temperarure
≥
DEFOFF).
Defrost max time of 12 minutes has elapsed.
1
2
RAM- , RAM- DEFROST TEMPERATURE
OUTDOOR (˚C)
-20
-10
10
20
0
0 -10 10 -20 20
HEA
T EX
CHANGER (
˚C)
DEFROST
START
TEMPERATURE
DEFROST END
TEMPERATURE