Final answer:
The pressure of the refrigerant inside a sensing bulb changes with the temperature at the evaporator outlet, which is crucial for temperature-dependent controls in refrigeration systems.
Step-by-step explanation:
The substance inside a sensing bulb that changes with the temperature at the evaporator outlet is A Pressure of the refrigerant. Sensing bulbs are part of a thermic diaphragm that detects temperature changes due to the pressure change in the refrigerant. As the temperature at the evaporator outlet increases, the refrigerant inside the sensing bulb heats up, which increases its pressure. Conversely, as the temperature decreases, the pressure inside the bulb drops. This pressure change is the primary mechanism for temperature-dependent controls in refrigeration systems such as the expansion valve which regulates the flow of the refrigerant based on the sensed pressure, thereby ensuring efficient operation of the air conditioning system.