Which of the following would not cause high head pressure in a refrigeration system?

A refrigerant undercharge refers to having too little refrigerant in the system, which typically leads to lower pressure in the evaporator and inadequate cooling. While it can cause issues such as reduced cooling performance and increased strain on the compressor, it does not contribute to high head pressure.

In contrast, an overcharge of refrigerant can result in excessive head pressure due to increased refrigerant volume in the system. Dirty condenser coils can impede proper heat exchange, raising the head pressure, while high ambient temperatures can increase the pressure as the condenser has to work harder to dissipate heat. Hence, among the options presented, refrigerant undercharge is the only factor that would not lead to high head pressure in a refrigeration system.