Fault Detection and Diagnostics for Rooftop Air Conditioners

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1. Evacuated the system, and then charged the system up to eighty per cent of nominal
refrigerant charge. The system ran for half an hour to reach steady state and then
data were logged.
2. After logging half an hour of low charge data, the condenser fouling fault was
added, by covering thirty per cent of condenser area using paper. At this time, there
were two simultaneous faults in the system: refrigerant low charge and condenser
fouling.
3. Half an hour later, a liquid line restriction fault was introduced by closing the
restriction valve until a twenty psi pressure drop was caused. Three faults existed in
the system simultaneously: refrigerant low charge, condenser fouling and liquid line
restriction.
4. Half an hour later, a compressor leakage fault was introduced by opening the
compressor bypass valve to let fifteen per cent of refrigerant mass flow rate bypass
the compressor. At this time, four faults existed simultaneously in the system:
refrigerant low charge, condenser fouling, liquid line restriction, and compressor
leakage.
5. The following steps describe the removal of faults,
6. 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.
7. 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.
8. 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.
9. Finally, half an hour later, the system was charged up to a nominal refrigerant level.
The system was supposed to run normally.