Which of the following could cause increased head pressure in an air conditioning system?

Increased head pressure in an air conditioning system is commonly linked to the conditions within the refrigerant circuit. When there is an overcharge of refrigerant, it leads to excess refrigerant in the system, which can result in higher pressures as the refrigerant needs to be compressed more to accommodate the additional volume. This can cause the compressor to work harder, potentially leading to inefficiencies and even damage over time.

The other factors listed may have implications for system performance but do not directly result in increased head pressure. Undercooling of refrigerant typically happens when the refrigerant does not lose enough heat before entering the metering device, which does not influence head pressure in the same way. Dirty evaporator coils can reduce the efficiency of heat exchange but usually lead to lower suction pressure, not increased head pressure. Lastly, an unclean air filter will restrict airflow, affecting cooling efficiency, though it is more likely to create issues with airflow temperature rather than direct pressure increases within the system. Therefore, the correct choice regarding increased head pressure is primarily and clearly linked to refrigerant overcharge.