**2.1. On/off capacity control**

The on/off capacity control is the simplest method adjusting the predetermined temperature (set point) using a thermostat. After the temperature reaches the set point, thermostat stops the compressor and circulating refrigerant in the cycle. Since the secondary fluid continues to circulate, the temperature of the water or air gradually raises. When the thermostat detects,

**Figure 2.** Capacity control methods [7].

this rise turns the compressor on. If the light-load conditions occur, this results on short cycling. Short cycling of the system reduces life of the compressor. In addition to that, the temperature of the secondary fluid fluctuates and uncomfortable conditions occur.
