A restaurant’s rooftop AC stopped cooling. Up on the roof, the reason was obvious the moment the access panel came off.

The evaporator coil was iced solid, face to face. Not a bit of frost along the bottom. The whole coil, and the filter section next to it.

An air conditioner ices for two reasons: not enough air over the coil, or not enough refrigerant in it. Either way the coil runs below freezing, the condensation on it freezes instead of draining, the ice blocks the air, which makes the coil colder, which makes more ice. Once it’s like this you can’t test anything. It has to thaw first.

Here the airflow side was the story. The 20x25x2 pleated filters had been in there a long time and were packed solid. Kill the airflow and the coil freezes.

We shut it down, thawed the coil, replaced the filters, cleared the drain, then checked charge on both circuits once it was running clean. Two compressors, both fine.

The follow-up a few days later, checking the actual numbers, is its own post. The lesson here is simple: a rooftop unit that’s iced isn’t broken. It’s telling you it’s been starved of air, and the filter is the cheapest thing on the roof.

If it heats or cools, we handle it. 📞 718-802-1700