Final answer:
A decrease in outdoor ambient temperature causes lower condensation temperature and pressure in an air conditioner with a fixed metering device, making the system less efficient as less refrigerant circulates.
Step-by-step explanation:
In an air conditioner with a fixed metering device, a decrease in the outdoor ambient temperature causes a decrease in the condensing temperature and pressure. This results in the working fluid spending more time in the condenser where heat transfer occurs as the gas condenses to a liquid. The reduced temperature causes the system's overall pressure to drop, and the air conditioner becomes less efficient because less refrigerant circulates through the system. During this process, the working fluid is cooled as it flows back through an expansion valve to the outdoor evaporator coils. In cold weather, however, some air conditioning systems act as heat pumps, and the direction of flow of the working fluid is reversed to draw heat from the outdoor air to warm the indoor space.