Ice on your AC lines or coil
Ice on an AC usually means too little warm air is crossing the indoor coil, from a dirty filter, blocked vents, or running in cool weather. If it keeps coming back with all of that ruled out, it is usually refrigerant, which only a technician can handle.
Also searched as: ac freezing up, ice on ac line, ice on ac unit outside, ac unit frozen over.
Every question and answer on this page, in order
Question 1: What kind of system is it, and when did you see the ice?
A heat pump has one outdoor unit that both heats and cools. If you're not sure, check whether the same system heats the house in winter.
- An AC, running in Cool mode: go to question 2
- A heat pump in Heat mode during cold weather: Probably normal: heat pump defrost
Question 2: Has it frozen before, even after you thawed it and changed the filter?
- Yes, it keeps refreezing: Likely cause: low refrigerant or a dirty coil
- No, or I haven't changed the filter yet: go to question 3
Question 3: How warm was it outside when it froze?
Lennox warns against running the AC when it's below about 60F outside.
- Cool, below about 60F: Likely cause: running the AC in cool weather
- Warm or hot: go to question 4
Question 4: How does the air filter look?
Slide the filter out and hold it up to a light.
- Gray or dusty, and little light comes through: Likely cause: a clogged air filter
- Clean, or changed in the last month: go to question 5
Question 5: Walk the house. Are the supply vents and return grilles open and clear?
Return grilles are the larger grilles with no louvers that pull air back to the system.
- Some are closed, or blocked by furniture, rugs or curtains: Likely cause: blocked vents or return grilles
- All open and clear: Likely cause: low refrigerant or a dirty coil
Possible results
Need the words for the phone call? Build a what-to-tell-the-technician checklist, or read when to call an hvac pro.