If the low side pressure is higher than normal and the high side pressure is lower than normal in heating mode, what is the most likely cause?

In heating mode, a heat pump operates by transferring heat from the outdoors to the indoors. The system relies on the proper functioning of components like check valves to maintain the correct pressure and flow of refrigerant. If the low side pressure is higher than normal and the high side pressure is lower than normal, this indicates a disruption in the typical refrigerant flow path.

A stuck open check valve at the outdoor coil allows the refrigerant to bypass the intended flow direction. This situation can lead to excessive low-side pressure because refrigerant is not being adequately compressed or moved through the system, resulting in an imbalanced pressure reading. The high side pressure being lower than normal is a consequence of this disruption, as the refrigerant is unable to cycle properly through the compressor and evaporator.

In contrast, other potential causes, like a faulty expansion valve, may lead to issues with refrigerant metering rather than creating the specific pressure scenario described. Similarly, a refrigerant leak would typically manifest as low pressure on both sides rather than the described high low-side and low high-side pressures, and a stuck open check valve at the indoor unit would mainly impact the returns rather than introducing the symptoms observed in the outdoor coil. Thus, a stuck open check valve at the outdoor coil