What is wrong? › Commercial HVAC
Clogged filters choke the unit and can freeze the coil
Restricted airflow makes the evaporator coil ice up, and a unit run frozen for hours can damage the compressor.
What is probably happening
- Filters loaded with dust, grease or construction debris, cutting airflow so the coil gets too cold and ices over.
- Ice on the coil then blocks what airflow is left, so the vents blow weak and barely cool.
- In a restaurant, grease from the kitchen loads filters much faster than an office.
Do this in the next five minutes
- Turn the system to Off at the thermostat and set the fan to On. Let the fan run to thaw any ice for 2 to 3 hours.
- If the filters are reachable from inside (a return grille or an air handler in a closet), change them now. Note the size printed on the frame.
- If the filters are inside the rooftop unit, leave them for the contractor. Do not go on the roof.
- Once thawed, turn cooling back on and check the vents. If it holds, book a maintenance visit.
- Put filter changes on a calendar: monthly in a kitchen, every one to three months elsewhere.
Do not
- Do not run cooling with ice on the coil. Thaw first.
- Do not run the unit with no filter in it. Debris goes straight into the coil and the cost goes up.
- Do not use a thicker or higher rated filter than the unit was designed for without asking. It can restrict airflow just like a dirty one.
Who to call
A licensed commercial HVAC contractor, if the unit does not recover after thawing
Filter changes are yours to do. If the coil keeps icing with clean filters, the cause is low refrigerant or a fan problem and that needs an EPA Section 608 certified technician.
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What it should cost
$100 to $250
Service call if the unit needs a technician after a filter change; the Department of Energy puts the energy saving from a clean filter at 5 to 15 percent
Source: Angi, HVAC repair cost, updated August 2026; US DOE Energy Saver. View source
National published range, not a quote for your job. The full cost table for this trade is on the commercial hvac page.
Ask this contractor, on the phone, before anyone comes out
Tap each one as you ask it.
- What filter size and rating does this unit take, and how many?
- Was the coil iced, and did you find the cause beyond the filters?
- Can you clean the evaporator and condenser coils on the same visit, and what does that add?
- How often should filters be changed for my type of business?
End the call if
- A refrigerant top up with no leak search. Refrigerant does not get used up; if it is low there is a leak.
- A quote for coil replacement with no photo of the coil.