Which pressures does an oil pressure differential switch use to open the contacts to the time delay heater?

The correct choice involves the relationship between system suction and discharge pressures in the context of an oil pressure differential switch. These switches are designed to monitor the pressure difference between the suction side (low pressure) and discharge side (high pressure) of the refrigeration system to ensure that the oil circulation is adequate and that the compressor operates safely.

When the oil pressure differential switch detects a certain pressure difference between these two points—meaning the oil pressure is too low—it will activate the time delay heater. This heater warms the oil to ensure it flows properly and lubricates the compressor effectively. By utilizing the suction and discharge pressures, the switch can reliably detect a drop in oil pressure that may indicate a potential problem with the oil flow, ensuring the safety and reliability of the refrigeration system.

The other options either refer to pressures or components not directly associated with the functioning of the oil pressure differential switch concerning the time delay heater. For instance, using the sensing bulb typically pertains more to temperature rather than pressure, and references to crankcase or oil pump discharge pressure don't relate to the basic operational function of this switch in managing oil pressure within the system.