Midea Precision AC Technical Manual MCAC-PDSM-2013-01
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situation of the system. When the water content of system is more than the standard, the liquid sight
glass basic color will change from green to yellow. When the refrigeration system has malfunction,
judge the error according to some operating parameters of the system.
When the suction pressure drops to below the set value of low pressure switch, it could lead to
the compressor stops. On the other aspect, high suction pressure also can be reduced to cool
the compressor motor, which may cause compressor damage.
Discharge pressure may be increased or decreased for the load conditions or the efficiency of
the condenser. When the discharge pressure reaches the setting value of the low pressure
switch, the high voltage switch action will make the compressor stop.
Thermal expansion valve can adjust the suction overheat degree. The suction overheat degree
has great influence for the using life of compressor, if the compressor operates on the situations
of too small or no suction overheat degree for long time, it may be directly led to compressor
produced liquid strike, which will crush the scroll compressor. Follow the below operations to
confirm the suction overheat degree of system:
1. Measure the suction wall temperature in the thermal expansion valve temperature sensing
position.
2. Take the compressor suction pressure sample from the needle valve of suction pipe.
3. Estimate the pressure difference between the temperature sensing position and the needle
valve of suction pipe.
4. The sum total of above two pressure plus one local standard atmospheric pressure value,
then find out the corresponding saturated temperature of the saturation pressure.
5. The suction overheat degree is the difference of the suction temperature and this saturated
temperature.
7.8 Compressor monitoring and replacement
This precision air conditioning system uses high efficient scroll compressor, which has high reliability.
If the project construction strictly accord with the correct program operations, then the probability of
failure which appears in operation process is very small.
If the problems which may result in compressor error can be early detected and corrected, then
most of the compressor errors can be avoided. So it is suggested that customer should regularly
contact the service of manufacture to do compressor operation state test, and do the monitoring
records.
During the compressor monitoring, check whether all electrical components of compressor are
running normally.
1. Check whether the corresponding air switches and contactor of the compressor are sensitive
and normal.
2. Check whether the high and low pressure switches are sensitive and normal.
3. Check whether the upper discharge temperature switch of the compressor has been fixed
reliably and done the thermal insulation.
4. Check whether the compressor wiring terminals resistance value is normal and the
grounding insulation is normal.
If for neglecting the inspection or other reasons to cause the compressor error, then before
changing the compressor it must be carefully do the fault analysis, the common errors mainly to
be the following two aspect:
