The cheapest repair on your walk-in is a clean coil

Every walk-in, reach-in, prep table and ice machine has a condenser coil. It's the grid of thin metal fins behind a grille or up on the roof, with a fan blowing through it. Its job is to throw off the heat the unit pulls out of the box.

Air has to move through those fins for that to work. Anything that coats them gets in the way: dust, grease, flour, lint, smoke, even mildew. A layer of dirt acts like a blanket. The heat stays trapped.

When the coil can't shed heat, the pressure and temperature inside the system climb. The compressor runs longer and hotter to keep the box cold. Here's how it shows up:

• The unit runs and runs and never seems to shut off.
• The box holds 38°F in the morning and creeps toward 45°F in the afternoon.
• Ice comes slow, or the machine stops making it.
• The power bill goes up with nothing else changed.
• The compressor is too hot to touch.

Run that way long enough and the compressor quits. That's the big repair, and it tends to happen on the hottest day of the summer, when the coil is working hardest. A coil cleaning costs a fraction of it.

Food is the other cost. Cold food has to stay at 41°F or below. If it sits above 41°F for more than four hours, it gets thrown out.

A coil near the fryers or the grill pulls in grease with the air. Grease grabs dust, and the two bake into a mat. A bakery or pizza kitchen gets flour in the fins. Rooftop condensers in the city collect more grit, leaves and cottonwood than ones out in open country.

Where the unit sits matters too. Boxes stacked against a reach-in grille can choke it. So can a condenser jammed into a hot, closed room. Neither one can breathe, even with a clean coil.

Check your unit's manual first. Many manufacturers call for a cleaning every few months, and that's the longest you should let it go. A unit next to the fryers may need it every month. A walk-in condenser on the roof needs a look in spring, before the heat comes.

Here's a simple rule. If you can see dust or grease on the fins, the cleaning is past due.

Your crew can keep reach-in and prep table grilles clear. Here's the safe way to do it:

• Turn the power off at the switch or breaker first.
• Use a soft brush and stroke along the fins, never across them.
• Vacuum the loose dirt off.
• Keep the grille and the space around it clear of boxes.

Leave the rest to a technician. Greasy coils need a coil cleaner and a rinse that keeps water off the electrical parts. Bent fins need combing straight. Walk-in and rooftop condensers mean ladders and live wiring.

On a maintenance visit we clean the coils and check refrigerant pressures. That's how we catch a weak compressor or a slow leak while it's still a small fix.