If the thermostat contacts are closed, and the compressor and condenser fan motor are not running while the blower motor is running, what might be the issue?

When the thermostat contacts are closed but the compressor and condenser fan motor are not operational while the blower motor is running, the situation often indicates an issue somewhere between the power source to the compressor and the necessary conditions for it to run.

The correct choice points to the possibility that safety devices, such as high-pressure (hp) and low-pressure (lp) switches, overload protection, or an oil pressure switch are open. These safety mechanisms are designed to prevent the compressor from running under unsafe conditions. For instance, if the refrigerant pressure is too high or too low, or if the compressor is drawing too much current, these switches will interrupt the circuit to protect the compressor from damage. The blower motor operates independently and continues to run because it is not dependent on these safety interlocks.

In this scenario, the closed thermostat contacts indicate that the control signal is present, meaning that the issue does not lie with the thermostat or the control circuitry itself, but rather with the safety conditions that must be met for the compressor to operate. Understanding this helps troubleshoot the system effectively, as investigating the safety switches would be the appropriate step forward.