Fault Detection and Diagnostics for Rooftop Air Conditioners

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NonCond
CondFoul
CompLeak
EvapFoul
LL-Restr
COMP-OFF
CONDENSER
COMP-ON
COMPRESSOR
EVAPORATOR
LIQUID-LINE
∆ T sat
∆ m&
ca
∆ T dis
∆ m&
ea
2
∆ P ll
Figure 1-14 Actual Decoupling Scheme of Component-Level Faults without Refrigerant
Mass Flow Measurement
1.2.4 Decoupling System-Level Faults
This section interprets relationships among the three system-level faults:
refrigerant overcharge, refrigerant undercharge and refrigerant leakage. Although these
three faults are system-level faults, from the classification criteria of fault cause,
refrigerant overcharge and undercharge faults are service faults while refrigerant leakage
is an operational fault. Service faults only happen during service and fault severity would
not change, while operational faults normally develop during operation and they would
deteriorate. This information contributes to the development of an FDD technique.
From the viewpoint of fault effect, refrigerant undercharge and refrigerant leakage
have the same fault effect on the system, low or deficient refrigerant charge, so they can
be considered as a single fault when doing fault detection and then can be separated using
the fault cause criteria when doing fault diagnosis. Physically, refrigerant deficient and
excessive charge faults would not happen simultaneously, so actually there is no coupling
among the three system-level faults at all from the sense of fault detection and it is pretty
easy to separate them using the fault cause criteria from the sense of fault diagnosis.
Figure 1-15 depicts the decoupling scheme for the system-level faults.
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