Which of the following can cause lower than normal suction pressure?

A restricted drier can indeed cause lower than normal suction pressure in an air conditioning system. The function of a drier, particularly when it is a liquid line drier, is to remove moisture and contaminants from the refrigerant before it enters the expansion device. When the drier becomes restricted, it can create a bottleneck that impedes the flow of refrigerant. This restriction means that less refrigerant is reaching the evaporator coil, leading to a drop in the suction pressure. Consequently, the system does not have enough refrigerant vapor present to maintain normal suction levels, which can impact overall system performance and efficiency.

Other factors, like a dirty condenser or an overcharge of refrigerant, can lead to different issues within the system, such as increased pressures or reduced efficiency, but they do not specifically account for lower suction pressure in the same way that a restricted drier does. Similarly, a high heat load can increase the pressure on the suction side but usually does not result in lower suction pressure. Understanding this relationship is critical for diagnosing and maintaining optimal system performance.