Frozen coil traced to restricted airflow, not evaporator fault

What we found

Ice on the coil or pipe can point to several causes. We checked airflow first before looking at the refrigerant side.

• Blower wheel heavily caked with dust and debris. Airflow across the evaporator coil was greatly reduced.
• Ice had formed on the evaporator coil surface, mostly where airflow was lowest.
• After defrosting and checking the coil fins, no damage or corrosion was found on the coil itself.
• Refrigerant pressures checked after blower cleaning. Readings returned to normal range without any gas work.

The blower wheel had built up heavy deposits over several years of use without chemical cleaning. The blower could not push enough air across the evaporator coil. The coil surface temperature dropped below freezing and ice formed. The coil itself was in working condition.

What we did

A chemical overhaul to deep-clean the blower wheel, fan barrel, and coil surface would restore airflow. No parts replacement was needed. The evaporator coil was intact.

After chemical overhaul, airflow was restored and the coil operated at normal temperature with no ice formation. The unit resumed cooling the room without any parts replaced.

What we learned

Frozen coil — refrigerant fault vs airflow fault.

• A frozen evaporator coil does not always mean the coil or refrigerant circuit is faulty. Reduced airflow across the coil surface drops its temperature below freezing point. Ice then forms on the coil.
• The most common cause of restricted airflow is a clogged blower wheel or choked filter. Checking these first takes less time than refrigerant testing. It also avoids needless part replacement.
• If cleaning restores normal airflow and the coil stops freezing, the coil itself was never the problem.