What does it indicate if an HVAC system is short-cycling?

When an HVAC system is short-cycling, it means that the system is turning on and off frequently in short intervals rather than running its full cycle. This behavior indicates that there may be issues in the system, particularly with the thermostat or possibly the size of the unit. If the system is oversized, it can reach the desired temperature too quickly and shut off before adequately circulating air throughout the space. A malfunctioning thermostat may also cause the system to misread temperatures or fail to regulate the system properly, leading to frequent cycling.

In contrast, the other options suggest outcomes that do not reflect the realities of short-cycling. Operating efficiently and improving air quality would not be associated with frequent on-off cycling; rather, these are generally signs of a well-functioning HVAC system. Excessive energy use may be a consequence of short-cycling, but it does not identify the underlying issue, such as the thermostat malfunction or improper sizing of the unit, which are central to diagnosing the root causes of this problem.