Restricted airflow
Dirty filters, blocked returns, undersized ducts, closed dampers, or blower problems can reduce airflow across the coil and let ice build up.
HVAC/R AI Pro
Frozen coil diagnosis
HVAC Field Guide
Why is my AC freezing up?
A frozen AC is often an airflow or refrigerant problem showing up at the evaporator coil. The fix depends on proving why the coil temperature dropped below freezing.
Field workflow
What this guide covers.
Learn why an AC freezes up, the most common causes, and how HVAC technicians diagnose airflow and refrigerant issues in the field.
Refrigerant conditions
Low refrigerant from a leak can reduce evaporator pressure and temperature. Superheat and subcooling readings help determine whether the charge or metering side needs attention.
System restrictions
Duct sizing, static pressure, and blower performance all matter. A frozen coil diagnosis should include the air side before replacing parts.
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