It surprises a lot of managers: the walk-in cooler or freezer runs fine all summer, then starts warming up, icing up or shutting off once Calgary hits -20°C. The cold outside should make the job easier, but the condensing unit on the roof or outside wall was built to get rid of heat, and very cold air brings its own problems. Snow, ice and missing or failed cold-weather controls are behind many winter service calls.
Why cold weather causes trouble
- Pressure drops too low: a refrigeration system needs enough pressure on the high side to push refrigerant through to the evaporator inside the box. In deep cold, the outdoor coil can cool the refrigerant so much that pressure falls off. The box can run warm, the coil inside can ice up, and the unit can shut off on its low-pressure safety.
- Cold-weather controls that failed or were never set up: units that run year-round outdoors rely on controls that slow or stop the condenser fans, or hold refrigerant back in the coil, to keep pressure up in winter. If one of these fails, the unit acts up only when it is cold.
- Crankcase heater problems: a small heater keeps the compressor warm when it is off. If it fails, liquid refrigerant can settle in the compressor, which can damage it on start-up.
- Snow and ice on the unit: drifting snow, ice falling from a roof edge, or water dripping from above and freezing can block the coil, jam the fan blades or bend them.
- Short cycling: a unit that keeps tripping off and restarting in the cold puts extra wear on the compressor and contactor.
What managers can check safely
- Box temperature: check the thermometer in the walk-in at opening and again in the afternoon, and write it down. A box that drifts warm on the coldest days is a strong clue.
- Ice inside the box: frost or ice building on the evaporator coil, or a freezer that won't defrost properly, can be a winter pressure problem. See why walk-in freezers ice up.
- Ground-level units: if the condensing unit sits on a pad behind the building, keep snow cleared back from it and don't let plows or shovels pile snow against it. Brush loose snow away gently. Never chip ice off the coil or fins; they bend and puncture easily.
- Unusual sounds: scraping or rattling from the unit often means ice is hitting the fan blades.
Leave rooftop units to a technician. Winter roofs are icy, and condensing units have fans and live electrical parts that can start without warning.
When to call a technician
- The walk-in runs warm or ices up mostly on cold days.
- The unit keeps shutting off and restarting, or won't start at all.
- Fans are frozen in place, bent or noisy.
- Ice has built up on the unit from water dripping above it.
- The breaker or disconnect for the unit keeps tripping.
If the breaker is the problem, our article on coolers and freezers that keep tripping the breaker explains what to check and when to leave it off.
Get ahead of it in the fall
A fall maintenance visit is the best time to test cold-weather controls and crankcase heaters, clean the condenser, and look for spots where water drips onto the unit or snow drifts against it. Our walk-in cooler and freezer maintenance checklist covers what a visit should include.
Keep your walk-in cold all winter
YYC Mechanical services walk-in coolers and freezers for restaurants, grocery stores and commercial kitchens across Calgary and nearby towns. If your walk-in is warming up and product is at risk, call our 24/7 emergency line.