Hitachi RAM-55QH5, Service Manual

Page: 60 / 108

– 69 –
PROCESSING AT OVERHEAT THERMISTOR (OH) HIGH TEMPERATURE
Restriction Start Conditions
If any expansion valve is operated at 480 pulses and the OH temperature > [NDOWN_ON], the compressor speed will be
reduced at a rate of 100 min
-1
/30 seconds.
The restriction will be released when OH temperature < [NDOWN_OFF], and the compressor speed will be increased at a
rate of 50 min
-1
/30 seconds to restore the target speed.
This reduced rotation speed is based on the speed when the reduction started, and will be maintained until the reduction is
finished. However, the reference speed will be exchanged only if the target speed is lower than the speed when the
reduction started.
If [NDOWN_OFF] ≤ OH temperature ≤ [NDOWN_ON] and the OH temperature does not rise from that 20 seconds
before, the reduction of compressor speed will not occur.
Restriction Release Condition (in common for all)
When two units are operated for heating:
Operation with one unit in heating or cooling mode and with two units in cooling mode is the same as in the above diagram.
WMAX2 and MINRPM are EEPROM data.
Unit 1
Unit 2
520
480
0
520
480
0
Electric expansion valve
Compressor
rotation speed
Heating output
[EDWN_ON]
[EDWN_OFF]
Cooling output
Outdoor fan
Turns on
for cooling
Compressor
Reversing valve
OH temperature
Unit 1
Unit 2
Hold
Hold 500ms
Hold
Hold 500ms
20 sec. 20 sec. 20 sec. 20 sec. 20 sec.
WMAX2
WMAX2
MINRPM
Decreases by 100 min
-1
/30sec. Increases by 50 min
-1
/30sec.
MODEL RAM-55QH5