Fault Detection and Diagnostics for Rooftop Air Conditioners

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bypass the compressor. At this time, four faults existed simultaneously in the
system: refrigerant low charge, condenser fouling, liquid line restriction, and
compressor leakage.
The following steps describe the removal of faults,
5. After the system ran for half an hour under four faults, the paper covering the
condenser was removed. There existed three simultaneous faults in the system:
refrigerant low charge, liquid line restriction, and compressor leakage, which is
a different combination than step three.
6. Half an hour later, the liquid line restriction fault was removed by fully opening
the liquid line restriction valve. At this time, refrigerant low charge and
compressor leakage existed in the system, which is a different combination than
step two.
7. Half an hour later, the compressor bypass valve was closed to remove
compressor leakage fault. There was only refrigerant low charge fault in the
system.
8. Finally, half an hour later, the system was charged up to a nominal refrigerant
level. The system was supposed to run normally.
2.2.2 Fault Detection and Diagnosis Window
This window plots the normalized fault indicator for four individual faults using
color bars: refrigerant low charge (Low-Charge), condenser fouling (Cond-Foul), liquid
line restriction (LL-Restr), and compressor leakage (Comp-Leak).
The normalized fault indicator is the ratio of the current feature value to the
predefined value, which is defined at an individual fault level causing 20% cooling
capacity degradation.
Normalized
_ Fault _ Indicator =
current _ feature − value
predefined _ feature _ value
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