Automotive Service Excellence (ASE) Air Conditioner Certification Practice Exam 2025 – Your All-in-One Guide to Exam Success!

A low pressure reading paired with frost on the inlet side of the thermal expansion valve (TXV) indicates that there is insufficient refrigerant flow through the system. The presence of frost suggests that the temperature at the inlet of the TXV has reached a point below freezing, which is generally a result of low refrigerant entering the valve.

When the TXV is stuck closed or if there is a clogged screen, the flow of refrigerant is restricted. As a result, the low pressure side of the system does not experience the standard refrigerant flow it needs to maintain proper pressure. This condition causes the refrigerant to evaporate too quickly or at too low of a pressure, resulting in the frosting effect due to the low temperature.

By understanding this dynamic, we recognize that the reading of low pressure combined with frost indicates that the refrigerant is not circulating properly, pointing specifically to potential blockages or a malfunctioning TXV that restricts the refrigerant flow into the evaporator. This condition is critical to identify, as it directly impacts the overall performance and efficiency of the air conditioning system.