Hitachi RAM-50CNHZ2, Service Manual, Page: 52 / 107

– 60 –
DEFROST
●
Reversing valve defrost system is employed: it consists of balancing period
→
reversing cycle period
→
balancing period.
(1)Defrost start condition
●
When all the following conditions are established, defrost is executed:
1
Normal operation
2
Heat exchange temperature is within defrost range specified by outdoor temperature and heat
exchange temerature.
3
Defrost inhibit period linked to outdoor temperature has passed.
(2)Defrost release condition
●
If any one of the following conditions is established, defrost is released:
1
Heat exchange temperature returns (heat exchange temperature
⭌
DEFOFF).
2
Defrost max time of 12 minutes has elapsed.
●
Released by condition
1
during balancing period: When remaining balancing period has elapsed,
returned to initial condition (ASTUS = 0).
●
Released by condition
1
or
2
during reversing cycle period: Shifted to balancing period.
(3)Outputs during defrost
●
Indoor defrost request: Transmitted to all units being operated in heating mode.
●
Compresor: Balancing period for [TDF414] seconds
→
Starting of reversing cycle period by [SDRCT2]
min
-1
for [TSKTM2] seconds
→
Accelerating by [DFCTEP] min
-1
/ [TDFSPT] seconds in
remaining reversing cycle period until defrost MAX speed [DEFMAX] is reached
→
Balancing period for [TDF415] seconds
●
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].