Refrigerated display case troubleshooting, symptom by symptom

By Vimal Bhaya, Founder and Lead Systems Architect · Last reviewed 7 October 2026

This is a continuation of Reach-ins, prep tables, display cases and reefers, a 10-part tutorial. You are on part 8 of 10.

Six symptoms cover most display case problems

Find what you are seeing, then jump to its section. Reasons are listed in roughly the order the makers' manuals, ACHR News and our failure-mode reference put them. Nobody publishes how often each fault happens in the field.

Here is a list of six things you can check to assess a display case's health

None of these needs a tool or an open panel.

1. The load line. Look at the line on the end panels, the honeycomb at the top and the return grille at the bottom. Should be: no product past the line, and nothing on either grille.
2. Drafts. Should be: nothing blowing across the front. Structural Concepts asks for 10 feet (3 m) from ceiling air vents, 15 feet (4.5 m) from outside doors and 5 feet (1.5 m) from windows.
3. The night curtain. Should be: pulled all the way down and hooked at close.
4. The warm readings. Note the times. Should be: lined up with the defrost schedule: 1 to 6 defrosts a day by case type, most ending in 20 to 30 minutes.
5. The cases next to it. Should be: holding. On a supermarket rack, if they are warm too, the fault is probably away from this case.
6. On a self-contained case, the condenser. Should be: a clear grille and light through the coil. Hussmann asks for a cleaning once a month.

Leave the EPR valves, the rack, refrigerant and the electrical panels to your refrigeration contractor.

1. A display case that will not hold temperature is most often loaded past its line, or its air curtain is broken

The product reads warm, the case display reads high, or shoppers complain. Before calling, rule out the causes that are not broken parts.

Reason 1: Product stacked past the load line warms, and warms the case

• Parts: none. How it is stocked is the problem.
• What happens: Hill Phoenix says overloading causes a loss of proper temperature, and that product past the load line will not be properly refrigerated. Product in the curtain's path also breaks the curtain for the rest of the case.
• The proof: the warmest product is at the front or the top, in the fullest case.
• Check: pull product back inside the line and 1 to 2 inches (2.5 to 5 cm) below each shelf.
• What to do next: Probe what sat past the line, and move anything above 41°F (5°C) somewhere cold. If the case stays warm with the line clear, try the bag test in reason 2.

Reason 2: A broken air curtain lets the store in

• Parts: honeycomb, return grille, fans.
• What happens: Signs, baskets, a blocked return grille, an iced coil, a dead fan or a draft all break the curtain. See symptom 3.
• The proof: warm at the front and top, with the back of the case cold.
• Check: the plastic bag test in symptom 3.
• What to do next: Front and top product that probes above 41°F (5°C) goes somewhere cold first. If the bag is drawn in, work through symptom 3 to find the gap.

Reason 3: Warm stock loaded into the case never catches up

• Parts: none. The stock is the problem.
• What happens: Display cases hold product at the temperature it arrives, ACHR News says. Structural Concepts' first fix for a case that will not hold is to chill the product before it goes in.
• The proof: warm after restocking, recovering slowly when left alone.
• Check: probe new stock before it goes in.
• What to do next: Keep stock above 41°F (5°C) out of the case, under your food safety plan. If stock goes in cold and the case still lags, look at reasons 4 to 6.

Reason 4: A night curtain left up, or torn, loses the overnight recovery

• Parts: night curtain.
• What happens: The night curtain cuts the warm air while the store is closed. Left up, the case works all night and starts the day warmer, and the coil collects more frost.
• The proof: warm first thing in the morning, every morning.
• Check: check the curtain is pulled all the way down and hooked at close, and is not torn.
• What to do next: At opening, probe the product and move anything above 41°F (5°C) somewhere cold. Add the curtain to the closing checklist, and have a torn one replaced this week.

Reason 5: A dirty condenser on a self-contained case cuts its capacity

• Parts: condenser coil.
• What happens: Hussmann says a dirty condenser blocks the airflow through the coils and affects the case's temperature.
• The proof: warm on busy, warm afternoons first, then more of the time.
• Check: look through the grille with a torch. Hussmann says to clean it at least monthly.
• What to do next: Deal with the food first: anything that probes above 41°F (5°C) goes somewhere cold. If the condenser is furred, switch the case off, then clean it as the manual says or book a cleaning.

Reason 6: On a rack, a valve set wrong or a group fault warms the case

• Parts: EPR valve, case valve, the rack.
• What happens: Each case circuit has a valve that holds its coil temperature. HVAC School says a pressure regulator set wrong makes the case run warm, or too cold so the coil ices. If every case on one rack group warms together, the fault is in the group, not the case.
• The proof: one case warm with its neighbours fine points to that case. Several warm together point to the rack.
• Check: compare it with the cases next to it, and tell your contractor which ones are warm.
• What to do next: Probe the warm cases and move product above 41°F (5°C) into cold storage. Call your refrigeration contractor today, say if one case or several are warm, and leave the valves to them.

Less often: a store above the case's design conditions of 75°F (24°C) and 55% humidity. And on drinks merchandisers owned by a bottler, an energy-saving device that raises the setpoint on a schedule, which looks like a fault but is the design. Convenience store monitoring covers that one.

Before you call, check these five things

1. Is any product past the load line or on a grille?
2. Is the warmest product at the front and top?
3. Was new stock loaded warm?
4. Are the neighbouring cases warm too?
5. Was the night curtain down overnight?

• When to call a technician: today if the product is above 41°F (5°C), or 4°C (39°F) in Ontario. Move it first. If several cases on one rack are warm, say so: it changes who comes.
• What to tell them: which cases are warm, how warm the product is, since when, and whether it lines up with deliveries, defrosts or store hours.

2. A display case that reads warm around its defrosts is usually normal, if it keeps to the schedule

The case display or a sensor reads in the 40s Fahrenheit a few times a day, then comes back down.

"Grocery store refrigerators around 45 degrees, is this normal"

r/foodsafety, thread title

During a defrost the coil is warmed until it reaches its end point, about 43°F to 48°F (6°C to 9°C) on medium-temperature cases in Hussmann's and Hill Phoenix's tables. An air sensor can be expected to read in the 40s Fahrenheit while that happens, though no maker publishes a normal reading. The product warms far less. Case controllers expect this, and delay or hide alarms through it: a Danfoss controller waits 90 minutes after a defrost before it will alarm.

So the question is not whether it reads warm. It is whether the warm reading comes on schedule and goes away. These are the reasons it might not:

Reason 1: A failed end-of-defrost sensor runs every defrost to its time limit

• Parts: termination sensor.
• What happens: Most defrosts end when a sensor says the coil is warm enough. If that sensor fails, the defrost runs to its time limit, which is longer. Hussmann says a defrost normally ends on temperature, well before its time limit.
• The proof: defrosts that are longer and warmer than they used to be.
• Check: time a few defrosts and compare them with last month.
• What to do next: After a long defrost, probe product and move anything above 41°F (5°C) somewhere cold. If defrosts now run longer than last month, book your refrigeration contractor this week with your timings.

Reason 2: A reset clock puts defrosts in shopping hours

• Parts: defrost clock, on the case controller or the rack.
• What happens: After a power cut, the defrost clock can restart at the wrong time. Defrosts then land in busy hours, where shoppers and staff see the warm readings.
• The proof: warm readings at a new time of day since a power cut, often across many cases at once.
• Check: check when the defrosts happen now, and whether that changed after an outage.
• What to do next: If the defrosts moved after a power cut, reset the case controller's clock the way its manual says. If the clock is on the rack, or you are not sure, ask your refrigeration contractor to reset it.

Reason 3: A blocked drain floods the coil after each defrost

• Parts: drain and trap.
• What happens: The defrost water has to drain away. If it backs up, it refreezes on the coil and the next defrost has more to melt.
• The proof: water in the bottom of the case after defrosts, and recovery getting slower.
• Check: look for standing water. See symptom 5.
• What to do next: If water stands in the case after defrosts, follow the drain steps in symptom 5. If the case is dry, the drain is probably fine: time the defrosts as in reason 1.

Before you call, check these four things

1. Do the warm readings line up with the defrost schedule?
2. Does it recover before your controller's post-defrost alarm delay ends? That is 90 minutes by default on a Danfoss EKC 202, an alarm setting rather than a recovery standard.
3. Are defrosts getting longer?
4. Was there a power cut before the timing changed?

• When to call a technician: only if the warm readings do not line up with the schedule, run longer than they used to, or do not recover. A normal defrost is not a fault.
• What to tell them: the times and lengths of the warm readings, and whether they changed after a power cut.

3. Warm top rows or a warm front mean the air curtain is broken

The back of the case is cold, but the product at the front or the top is warm. The curtain of cold air down the front has gaps, and the store's air is getting in.

Reason 1: Product, signs or baskets in the curtain's path break it

• Parts: none. What is in the way is the problem.
• What happens: Hussmann says air outlets and returns must stay clear, and that signs and racks it has not approved disturb the air. Structural Concepts says never to set product on the return grille.
• The proof: a gap in the cold air where something sticks out.
• Check: clear the honeycomb at the top and the return grille at the bottom.
• What to do next: Anything at the front that probes above 41°F (5°C) goes to other cold storage. From now on, keep both grilles bare and use only signs and racks the case maker approves.

Reason 2: A dirty or badly fitted honeycomb scatters the air

• Parts: honeycomb grille.
• What happens: The honeycomb straightens the air into a sheet. A Tyler manual warns that a badly installed honeycomb can cause poor airflow, and Hill Phoenix recommends cleaning the case, honeycomb included, once a week.
• The proof: a curtain that feels weak or patchy along the case.
• Check: look at the honeycomb, and clean it with spray detergent and a soft brush.
• What to do next: Check the front rows with a probe, moving anything above 41°F (5°C) somewhere cold. Then clean the honeycomb weekly with the case off, and have your contractor refit one that will not seat.

Reason 3: A draft from a vent, a fan or a door blows the curtain away

• Parts: none. The store's air is the problem.
• What happens: Structural Concepts says to keep cases 10 feet (3 m) from ceiling air vents and 15 feet (4.5 m) from outside doors, because air blowing on the front interrupts the curtain. Hussmann says not to let air conditioning, fans, open doors or windows make air currents round its cases.
• The proof: warm product near one end, or worse when the heating or air conditioning runs.
• Check: stand in front of the case and feel for moving air.
• What to do next: Probe the warm end first, and move anything above 41°F (5°C) somewhere cold. If you feel air moving, turn the fan away, keep the door shut or have the vent redirected.

Reason 4: An iced coil or a dead fan cannot push enough air

• Parts: coil, fans.
• What happens: ACHR News lists both as causes of a broken curtain. With less air coming out, the curtain falls short.
• The proof: weak air at the honeycomb along the whole case.
• Check: see symptom 4.
• What to do next: Probe along the case and move anything above 41°F (5°C) somewhere cold. Weak air along the whole case needs your contractor within a day: tell them if you can see ice.

The plastic bag test. ACHR News describes a simple check: hold a light plastic bag at the front of the case. If the bag is drawn into the case, ACHR News says, so is the store's air. A technician can go further, with a smoke test at the return grille and a meter that measures the air's speed against the case's specification.

Before you call, check these four things

1. Is anything sticking into the curtain, or on a grille?
2. Is the honeycomb clean and seated?
3. Is there a vent, fan or door blowing at the front?
4. Does the bag test show a gap?

• When to call a technician: this week, or today if product is warm. Most of these are fixed in store. Weak air along the whole case is a call.
• What to tell them: where the case is warm, what the bag test showed, and what is near the case.

4. Weak air from the honeycomb, or frost on the product, means an iced coil from wet store air or failing defrosts

Air from the honeycomb is weak, frost shows on the product or in the case, or the case slowly warms over days.

Reason 1: Store humidity above 55% loads the coil with frost

• Parts: none. The store's air is the problem.
• What happens: Oak Ridge National Laboratory reports that frost built up exponentially as store humidity rose. ACHR News says to keep store humidity to 55%, and that supermarket glass-door freezers run above their design conditions may develop frosting and icing problems.
• The proof: icing worst in summer and on humid days.
• Check: check the store's humidity, if the building system shows it.
• What to do next: If store humidity reads over 55 percent, take it up with whoever looks after the building's heating and cooling. Ice on the coil needs the case off to melt, with the product moved first: never chip it.

Reason 2: A broken curtain or a night curtain left up pulls in wet air

• Parts: air curtain, night curtain.
• What happens: More store air in the case means more water on the coil. See symptom 3.
• The proof: icing that follows a draft, overloading or a curtain left up.
• Check: fix the curtain first.
• What to do next: Once the curtain holds, make sure the night curtain goes down at every close. If frost still builds day after day, check the defrosts in reason 3.

Reason 3: Defrosts that are too few, or fail, leave frost behind

• Parts: defrost settings, heaters, termination.
• What happens: If the defrosts cannot clear the coil, each one leaves a little more. Some Danfoss controllers can warn of restricted airflow or an icing coil.
• The proof: frost that builds day after day.
• Check: check that defrosts happen on schedule.
• What to do next: If defrosts are missed or frost outlasts them, book your contractor within a day and give them the schedule. Until they come, keep probing, and move anything above 41°F (5°C) somewhere cold.

Reason 4: A pressure valve set too cold freezes the coil

• Parts: EPR valve.
• What happens: HVAC School says an EPR set too low makes the coil run too cold and ice. That is the contractor's adjustment.
• The proof: a case that runs colder than its neighbours and ices.
• Check: tell your contractor.
• What to do next: Book your refrigeration contractor within a day, and say this case runs colder than its neighbours and ices. Leave the valve to them, and do not chip at the ice while you wait.

Before you call, check these four things

1. Is it humid in the store?
2. Is the curtain whole, and the night curtain used?
3. Are defrosts happening on schedule?
4. Is the case colder than its neighbours?

• When to call a technician: within a day. Hill Phoenix's cleaning steps have the case turned off long enough to clear any frost or ice from the coil and pans, and an iced case needs the same. Move the product first, and do not chip the ice.
• What to tell them: where the ice is, the store's humidity if you know it, and the defrost schedule.

5. Water on the floor or in a display case usually means a clogged drain, a failed trap or an overflowing pan

Each defrost makes water that has to drain away, to a floor drain or, on a self-contained case, to a pan that evaporates it.

Reason 1: A clogged drain backs up into the case

• Parts: drain.
• What happens: Structural Concepts says to keep drains clean and free of debris, because a clog robs the case of refrigeration. Hill Phoenix says to check the waste outlet is not clogged before cleaning.
• The proof: water in the bottom of the case after defrosts.
• Check: look at the drain outlet in the bottom of the case.
• What to do next: If you see debris in the outlet, switch the case off before clearing it. If the outlet looks clear and water still stands, call your contractor: today if water reaches the floor.

Reason 2: A trap or an evaporating pan that has failed lets it out

• Parts: trap, condensate pan.
• What happens: Structural Concepts' checklist for water on the floor is the trap, power to the evaporating pan, and the store's humidity. Hussmann says missing base panels can make a self-contained case's pan overflow.
• The proof: water on the floor in front of or under the case.
• Check: check the base panels are in place, and look at the pan without touching it: its heater runs hot.
• What to do next: Put a sign out and mop up now, then switch the case off before refitting any missing base panel. With the panels on and water still coming, call your contractor today about the trap or pan power.

Reason 3: Cleaning water faster than the drain can take it

• Parts: none. How it is cleaned is the problem.
• What happens: Hill Phoenix says not to put water into the case faster than the drain can carry it away.
• The proof: water on the floor after cleaning only.
• Check: clean with less water.
• What to do next: For each clean, switch the case off, check the outlet is clear, and pour no faster than it drains. If water also appears after defrosts, go back to reasons 1 and 2.

Before you call, check these four things

1. Is the water in the case or on the floor?
2. Is the drain outlet clear?
3. Are the base panels in place?
4. Is it only after cleaning, or after defrosts?

• When to call a technician: today if water is on the sales floor, where people slip. Put out a sign and mop it up first.
• What to tell them: where the water is, and whether it follows defrosts or cleaning.

6. Glass doors that fog or sweat usually meet humid air, or their heaters are off

Shoppers cannot see the product, water runs down the glass, or frost forms on a freezer door's frame.

Reason 1: Door and frame heaters that are off or have failed

• Parts: anti-sweat heaters.
• What happens: Glass-door freezers run low-power heaters in the door frame and the glass. ACHR News describes one in the frame that stops the door freezing shut, and another in the door that stops the glass fogging. Many glass-door coolers have anti-sweat heaters too.
• The proof: fog or frost on one door, or on all of them since a setting changed.
• Check: a contractor's job, unless there is a heater switch you can see.
• What to do next: If a heater switch you can see is off, turn it on and watch whether the glass clears. Otherwise, book your contractor this week, and say which doors fog and whether the frames frost.

Reason 2: Store air more humid than the case was built for

• Parts: none. The store's air is the problem.
• What happens: ACHR News says glass-door freezers run above their design conditions may develop frosting and icing problems. Every door opening brings that air in.
• The proof: fog on humid days, across many doors.
• Check: check the store's humidity.
• What to do next: If the store reads above 55 percent humidity, take it up with the people who run its air conditioning. If it reads below that and the doors still fog, go back to the heaters in reason 1.

Reason 3: A door that does not seal lets warm air in at the edge

• Parts: door gasket, closer.
• What happens: A door that does not close fully, or a torn gasket, leaks warm, wet air at one edge, where it fogs or frosts.
• The proof: fog or frost along one edge of one door.
• Check: let the door close on its own, and look at the gasket.
• What to do next: If the door hangs open or its gasket is torn, get the closer or gasket fixed this week. Until then, have staff check that door is fully shut each time they pass.

Before you call, check these four things

1. Is it one door or all of them?
2. Is it only on humid days?
3. Does each door close and seal on its own?
4. Did a setting or a schedule change?

• When to call a technician: this week. A fogged door is a sales problem first, but a freezer door that frosts round its frame will soon stick.
• What to tell them: which doors, on which days, and whether the frames frost.

This is where TemperatureWise is different: it learns the defrosts and compares the cases

A threshold alarm on a display case goes off at every defrost, so staff learn to ignore it. The case controller avoids that by delaying its alarms after each defrost, by 90 minutes as standard on one Danfoss model. That also delays the alarm when something is really wrong.

TemperatureWise uses machine learning on the full temperature history of each case. It learns that case's own defrosts and store-hours pattern in its first week, so a normal defrost is not an alarm. When the pattern changes, such as defrosts that run longer, or a case that stops recovering, TemperatureWise tells you what has changed.

With a sensor in more than one case, it also shows when cases warm together, which points to the rack rather than the case, as grocery store monitoring explains. See how TemperatureWise works.