What is the impact of outdoor temperature rising above specified ranges on suction pressure in heating mode?

In heating mode, the suction pressure in an air-to-air heat pump is influenced significantly by the outdoor temperature. As the outdoor temperature increases and rises above specified ranges, the refrigerant captures more heat from the outside air, which leads to an increase in the vapor pressure of the refrigerant in the evaporator coil.

Higher outdoor temperatures enhance the efficiency of heat transfer, resulting in a greater volume of heat being absorbed. This absorption causes the refrigerant to vaporize more effectively, raising the suction pressure as the vapor moves back to the compressor. Essentially, warmer outdoor conditions allow the refrigerant to operate more efficiently, thus increasing the suction pressure.

This relationship succinctly explains why the correct answer highlights an increase in suction pressure; it is a natural consequence of the heat pump's design and function as it adapts to changes in ambient temperature while aiming to provide efficient heating.