Experimental study of liquid line temperature drop as a fault feature for detecting severe liquid line restrictions in residential air conditioning systems

Liquid line restrictions (LL) can occur in an air conditioning system in multiple ways, such as a clogged filter drier, kinked liquid line, etc., and impact the performance of the system. In this study, the objective is to test and refine fault diagnostic methods for LL faults. We tested the effects of four common installation faults in a laboratory - LL, improper evaporator airflow, improper refrigerant charge, and the presence of non-condensable gas in the refrigerant, singly and in combination. They were tested on a split residential heat pump and an air conditioner in cooling mode. The results are used to validate a method that uses the liquid line temperature drop caused by LL faults as a feature to detect LL faults. The sensitivity of this temperature drop to LL faults and other faults were also studied, so that an effective threshold for declaring an LL fault can be ascertained. The experiments are the first to show that this feature is effective in detecting LL faults even when multiple other faults are present, and that it does not cause false positives when no LL is present.