Frozen evaporator coil: guided troubleshooting
Ice on the indoor coil or the suction line in cooling. Answer each question from what you see on site.
Step 1
Has the coil been fully thawed?
Compressor off, blower on. Readings taken on an iced coil are meaningless.
Did this solve it?
See every step in this flow
- Has the coil been fully thawed? Compressor off, blower on. Readings taken on an iced coil are meaningless.
- Yes, it's thawed and dry: Is the indoor blower running at the right speed with a clean filter and coil?
- Not yet: Thaw it first
- Is the indoor blower running at the right speed with a clean filter and coil?
- No: dirty filter or coil, or blower problem: Low airflow
- Blower runs, but static pressure is high or registers are closed: Duct restriction
- Airflow checks out: Was it running at a low outdoor temperature, or with a very low indoor setpoint?
- Was it running at a low outdoor temperature, or with a very low indoor setpoint?
- Yes: Running outside its conditions
- No: Measure superheat and subcooling. What do you have?
- Measure superheat and subcooling. What do you have?
- High superheat, low subcooling: Low charge
- High superheat, normal or high subcooling: Restriction or metering device
- Both near target: Check how it runs over time
Where each path ends
Thaw it first
Turn the compressor off and run the blower until all the ice is gone, and watch the drain pan while it melts. Then start this flow again.
Low airflow
The most common cause. Replace the filter, clean the coil and blower wheel, and test the blower motor and capacitor.
Duct restriction
Measure total external static pressure against the blower's rating. Look for undersized returns, crushed flex, closed dampers and too many closed registers.
Running outside its conditions
Standard systems aren't meant to cool at low outdoor temperatures without a low-ambient kit, and a very low setpoint keeps the coil below freezing. Check the manufacturer's operating range.
Low charge
Low refrigerant drops the evaporator temperature below freezing. Find and repair the leak before adding refrigerant.
Restriction or metering device
A plugged filter drier or a TXV that isn't feeding starves the coil. Check for a temperature drop across the drier and test the TXV.
Check how it runs over time
If charge and airflow are right now, look for an intermittent cause: a blower that stops while the compressor keeps running, a contactor stuck closed, or a thermostat left on a very low setpoint.