3 Reasons Your Car's AC Keeps Freezing Up

Frozen evaporator coils are a problem that can plague any air conditioning system. Air conditioning engineerings design their systems to produce a certain amount of temperature drop at the evaporator coil. As the evaporator transfers heat to the refrigerant, the surrounding air temperature falls, and water condenses onto the coil.

However, the temperature must remain warm enough near the coil to prevent the condensate from freezing. Ice creates insulation over the coils, creating a condition commonly known as a frozen AC. If your car's air conditioning is freezing up, here are three of the most likely culprits for this frustrating and potentially damaging problem.

1. Refrigerant Leaks 

Refrigerant leaks can occur in any air conditioning system, but they're particularly common in automotive applications. The refrigerant lines in a home's central air conditioner are mostly inside and protected from the weather. In contrast, your car's refrigerant lines must contend with vibrations, engine heating, and cooling cycles, and constant exposure to the elements.

Checking your car's refrigerant level requires more than simply looking at a dipstick, so it's not a job you should attempt yourself. If you suspect low refrigerant levels, having a professional shop investigate the problem is the best plan. Remember that AC systems use sealed refrigerant lines, so any loss of refrigerant indicates an underlying leak that you'll need to address.

2. Refrigerant Restrictions

Any condition that reduces the amount of refrigerant that reaches the evaporator coil will, counterintuitively, produce lower temperatures. Refrigerant leaks are the most common reason for reduced pressure, but restrictions are another potential issue. A restriction in the system can reduce pressure at the evaporator, even though there's still plenty of refrigerant available.

A refrigerant restriction can often be even more challenging to diagnose than a refrigerant leak. Common locations for restrictions in automotive systems include the filter/dryer unit or the thermal expansion valve (TXV). The TXV's job is to control refrigerant pressure into the evaporator, and a faulty one can lead to reduced pressure and a frozen evaporator coil.

3. Faulty Blower Motors 

Automotive AC systems are surprisingly complex compared to home central air conditioners. Whereas many homes use single-stage blowers and one-speed compressors, automotive systems typically use variable-speed blowers and compressors. This design allows the system to provide varying cooling levels but introduces added complexity.

The blower serves an important role in the system to deliver cool air to the cabin and ensure a constant flow of warm air over the evaporator. A faulty blower motor may not provide sufficient airflow, resulting in an uncomfortably warm cabin while allowing the condensate to freeze on the evaporator coil. If you notice reduced airflow from your cabin vents, a faulty blower may be responsible for your frozen AC.

Contact a car air conditioning service to learn more.