Mitsubishi City Multi PURY-P400 Service Handbook page 45

(8) Judgement and control of refrigerant amount
• Judges refrigerant amount by detecting refrigerant liquid surface level in the accumulator.
1) Judgement of accumulator liquid level
• Return refrigerant from accumulator liquid level detecting circuit to compressor inlet pipe, detect piping tempera-
ture, and judge liquid level.
When heated with a heater, liquid refrigerant temperature is nearly equal to low pressure saturation temperature,
and gas refrigerant temperature is slightly higher than low-pressure saturation temperature. By comparing these
temperatures at the accumulator inlet, refrigerant liquid level can be determined.
Accumulator liquid level is judged in 3 steps as shown in the figure, from temperature A and liquid level detecting
temperatures (TH3, TH4). After deciding refrigerant status (Liquid: TH3 and TH4 are TH2 + 9°C or less, Gas: TH3
and TH4 are TH2 + 9°C or more), judge liquid level by comparing TH3 and TH4.
Balance pressure pipe
Inlet pipe
TH2
2) Control of liquid level detection
1 Prohibition of liquid level detection
Liquid level is detected in normal conditions except in the following conditions:
(Cooling)
• For 6 minutes after starting unit, and during unit stopping.
(Heating)
• During defrosting.
• For 10 minutes after refrigerant recovery.
(Note that liquid level determination is performed, even when liquid level detection is disregarded.)
2 In case AL = 2 has been detected for 3 consecutive minutes (control during excessive refrigerant replenishment
and error mode)
• Mode changes to intermittent fault check mode preceded by 3 minutes restart prevention. It is normal when the
discharge SH is high. Error stop is observed when trouble is detected again, the same intermittent fault check
mode is entered (for 30 minutes after unit stops for intermittent fault check).
• When turning on liquid level trouble disreguard switch (SW2-4), error stop is not observed, and 3 minutes restart
prevention by intermittent fault check mode is enforced. However, LED displays overflow.
(Turning SW2-4 on makes TH6 < outdoor air sensor > error ineffective.)
3 When operation mode shows "Stop," excessive or insufficient refrigerant display and excessive or insufficient
refrigerant ignore display are extinguished.
Dividing plate
TH4
TH3
–44–
*Temperature A: low pressure saturation temperature
(TH2).
AL=2
AL=1
AL=0
• Judgement by the AL is at best only a
rough guideline.
Outlet
Please do not add refrigerant based
pipe
on the AL reading alone.