Mitsubishi Electric CITY MULTI PQRY-P200YMF-B Service Handbook page 55

(7) Judgement and control of refrigerant amount
Judge refrigerant amount by detecting refrigerant liquid surface accumulator.
1) Judgement of accumulator liquid level
Return refrigerant from accumulator liquid level detecting circuit to compressor inlet pipe, detect piping temperature,
and judge liquid level.
When heated with heater, liquid refrigerant temperature is almost equal to low pressure saturation temperature, and
gas refrigerant temperature is a little higher than low pressure saturation temperature. By comparing these tempera-
tures with low pressure saturation temperature Te in accumulator inlet portion, refrigerant liquid level can be judged.
Accumulator liquid level is judged in 3 steps as shown in the figure, from low pressure saturation temperature Te
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.
Ps
Te (low pressure saturation
Temperature)
2) Control of refrigerant amount
Cooling
(a) Prohibition of liquid level detection
• Liquid level is detected in normal conditions except for the following:
For 6 minutes after starting unit, and during unit stopping.
(b) In case AL=2 and Td-Tc
excessive refrigerant replenishment and trouble mode)
• Changed to intermittent fault check mode preceded by 3 minutes restart prevention. Error stop is observed
when trouble is detected again in the same intermittent fault check mode (for 30 minutes after unit stops for
intermittent fault check).
• When turning on liquid level trouble ignore switch (SW2-6), error stop is not observed, and 3 minutes restart
prevention by intermittent fault check mode is repeated. However, LED displays overflow.
(Turning SW2-6 on makes the error of TH6 < outdoor air sensor > ineffective.)
(c) When operation mode shows "Stop", excessive or insufficient refrigerant display and excessive or insufficient
refrigerant ignore display are extinguished.
Heating
(a) Prohibition of liquid level detection
Liquid level is detected in normal conditions except for the following.
• For 6 minutes after starting unit, and during unit stopping (including restart after overflow ignored).
• During defrosting operations and for 6 minutes after defrosting.
20 is detected for 3 consecutive minutes during liquid level detection (control at
–52–
* Judgement by the AL is at best only a
rough guideline.
Please do not add refrigerant based on
the AL reading alone.