Conference Year



Non-condensable gas, Residential air source heat pump, Fault detection and diagnosis, Fault impacts, Simultaneous faults


Non-condensable gas (NC) introduced into a vapor compression air-conditioner or heat pump system by improper system evacuation during an installation or repair has negative impacts on the performance of the system. The NC’s partial pressure combines with the refrigerant pressure, increasing the condenser’s total pressure, hence increasing the compressor specific work, leading to reduced efficiency for the system. Although the impacts of NC can be significant and the fault is believed to be common, little research has been conducted on this fault, compared with other faults. This paper describes a study of NC faults that includes two experimental investigations. The first considers the impacts on performance at four operating conditions when NC faults are introduced to a fault-free system. The study also tests the impacts of NC when added to combinations of other types of faults. Laboratory test results from a 4-ton residential heat pump system are provided. This system was tested with NC at two intensity levels, in combination with: undercharge, overcharge, improper evaporator airflow, and liquid line restrictions. Combinations of two, three, and four simultaneous faults were tested. A second experimental investigation tests the accuracy of a field diagnostic method for NC faults, and a new diagnostic model is provided to quantify NC fault intensity in the field.