States that problems encountered in the maintenance of around 14 000 gas-engine heat pumps (GHPs) installed in Tokyo include many that could be instructive when gas engines are to be used as air conditioners. States that from an analysis of these cases, the causes of problems have been clarified and the countermeasures have been established so that the quality of GHPs provided with such countermeasures has been upgraded. Introduces countermeasures related to the gas engine, the refrigeration cycle and control system to highlight those points that should be considered in designing gas-engine heat pumps.

KEYWORDS: Heat pumps, gas engine heat pumps, maintenance, Japan, air conditioning, quality, designing, refrigeration, controls