Hitachi RAM-50CNHZ2, Service Manual, Page: 54 / 107

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AUTO-FRESH DEFROST
●
During heating operation is stopped, and when auto-fresh condition is established, defrost operation will be
performed while operation is stopped.
Auto-fresh consists of balancing period at start of defrost for [TDF414] seconds
→
Reverse cycle period for
MAX 12 minutes.
(1) Start conditions for auto-fresh
●
When all the following conditions are established, auto-fresh is executed:
1
Defrost request signal is present.
2
All indoor units are stopped.
3
15 minutes of auto-fresh inhibit period has elapsed.
4
Compressor is ON when operation is stopped.
5
Compressor delay command is sent from indoor unit when operation is stopped.
(2) Release condition of auto-fresh
●
If any one of following conditions is established, auto-fresh is released:
1
Heat exchange temperature returns (heat exchange temperature
⭌
DEFOFF)
2
12 minutes of defrost MAX time has elapsed.
3
Failure occurred.
4
Either unit 1 or unit 2 started operation.
❈
Released during start of balancing period: Stopped or started after remaining balancing period has
elapsed.
❈
Released during reverse cycle period : Stopped or started after balancing for 3 minutes.
(3) Outputs during auto-fresh
[Indoor unit defrost request]: Transmitted only to unit to which auto-fresh is applied 9indoor unit stopped
last).
[Compressor]: Accelerated by DFSTEP rpm/TDFSPT seconds and reaches defrost MAX speed [DEFMAX].
[Electric expansion valve]:
Unit auto-fresh not applied: FULL CLOSE when balancing for 30 seconds has elapsed at start of defrost.
Unit auto-fresh applied: Synchronized with step-up of rotation speed of compressor, opened by [pulses
and reaches MAX opening degree [DEFSMX] when rotation speed of compressor
reaches [DEFMAX].
(4) Note
●
Shifted to auto-fresh in defrost mode when operation is stopped.
●
All indoor units must be stopped to fulfill condition for auto-fresh.
If signal is delayed, auto-fresh condition will not be established.
DFSPPS Pulse
Defrosting signal
Unit 1
Unit 2
Unit 1
Unit 2
Unit 2
Unit 2
Unit 1
Unit 1
Turns on for
cooling
Cooling output
Heating output
Outdoor fan
Compressor
rotation speed
520
520
480
480
0
0
Electric expansion valve
Reversing
valve
Request
Compressor
Operation
Auto-fresh inhibit period 15min.
WMAX2
WMAX1
15sec.
Balancing period [TDF414] sec.
30sec. TSKTM2
SDRCT2
Reverse cycle period (max. 12 minutes)
Defrosting sequence
DFSTEPrpm/
TDFSPT sec.
DEFMAX
Balancing period 3min.
Balancing request
Balancing request Defrosting request
30sec.
80sec.
DFCTPS
Hold
Hold
Hold
Hold
30sec. 60sec.
PCLOSH
100rpm
DFPSMX