Which of the following factors does NOT cause a change in compressor capacity?

When considering the factors that affect the capacity of a compressor, it's important to understand how each of these elements directly influences the compressor's operation and efficiency.

Suction pressure plays a critical role in the performance of a compressor. As the suction pressure increases or decreases, it directly impacts the compressor's ability to draw in refrigerant vapor, which in turn affects the capacity. Similarly, discharge pressure affects the capacity as it determines how much pressure the compressor needs to overcome to push the refrigerant into the condenser. Changes in discharge pressure can thus directly modify the work done by the compressor, which influences its overall capacity.

Refrigerant vapor density is another factor that affects a compressor's capacity. The density of the refrigerant vapor is related to its pressure and temperature. When vapor density changes, it can affect the mass flow rate of the refrigerant entering the compressor, subsequently impacting the capacity as well.

In contrast, the thermostat setting does not influence the compressor's capacity directly. The thermostat primarily serves as a control mechanism to maintain the desired temperature within the conditioned space. While adjusting the thermostat setting may turn the compressor on or off (or adjust its speed in some systems), it does not intrinsically alter the physical properties of the refrigerant being compressed or the compressor