A little frost on the evaporator coil is normal. A coil turning into a block of ice isn't. Here are the seven causes we see most often, what your staff can check, and when it's time to call.
The evaporator is the finned coil with fans inside your walk-in. Its job is to pull heat out of the box. When ice builds up on it, air can't pass through, the coil can't absorb heat, and the cooler slowly warms up even though the compressor keeps running. Left long enough, you lose product.
Most of the time the ice is a symptom of something else. Fix the cause and the ice stops coming back.
This is the most common cause by far. Every time warm, humid air gets into the box, the moisture freezes onto the coil. A torn gasket, a sagging hinge, a weak door closer, or missing strip curtains can let in a surprising amount of air over a shift.
What to check: close the door on a sheet of paper at several points around the frame. If it slides out easily, the gasket isn't sealing there. Frost building up around the door frame is another giveaway.
Propping the door during deliveries or restocking has the same effect as a bad seal, only faster. A 20-minute delivery with the door wedged open can load the coil with ice that the next defrost cycle can't clear.
Walk-ins run scheduled defrost cycles to melt normal frost off the coil. If the defrost timer or controller fails, or a heater or defrost sensor goes bad, a little frost gets left behind each cycle and builds into solid ice over a few days.
If one of the fans on the evaporator isn't spinning, that section of coil stops getting airflow and ices over. Look up at the unit: every fan should be turning and you should feel air moving.
A leak lowers the refrigerant charge, which makes the coil run colder than it's designed to. Ice often starts on one part of the coil and spreads. Low refrigerant always means there's a leak somewhere, and finding and repairing it is a job for a licensed refrigeration technician.
Cases and boxes stacked right up against the evaporator, or shelving blocking the fans, stop air circulating properly. A coil clogged with dust does the same thing. Keep at least a hand's width of clear space in front of and around the unit.
Melted water from each defrost has to drain out of the box. If the drain line is blocked, or the heater that keeps it from freezing has failed, water sits in the drain pan and refreezes. You'll usually see ice building from the bottom of the coil up, or water dripping onto the floor.
Don't chip the ice off with a knife, screwdriver, or scraper. The coil tubing is thin, and one slip can puncture it and cause a refrigerant leak, turning a simple service call into a much bigger repair.
Most of these causes show up early on a routine maintenance visit: worn gaskets, weak door closers, dirty coils, failing fan motors, and defrost problems. Catching them on a scheduled visit costs far less than an emergency call and lost product. See how our maintenance contracts work.
Walk-in icing up right now? Text us at 604-217-6489, open 24/7. We service grocery stores, restaurants, and commercial kitchens from Hope to Whistler. More about our refrigeration service.