What it is

A display case is a refrigerated fixture built to keep product cold while customers see and grab it. The case design is a constant fight between two goals: show the product (open, well-lit, easy reach) and hold temperature (which wants a sealed, insulated box). Where a case lands on that spectrum decides how hard its evaporator works, how fast it frosts, and therefore how it has to defrost.

You'll run into a handful of standard styles, and knowing the style tells you a lot before you even open a panel.

How it works

Open multideck (vertical, no doors). Produce, dairy, deli grab-and-go, packaged meat. Cold air is blown down a back panel and across the shelves, and an air curtain of cold air falls across the open front to hold the cold in. These cases are infiltration machines — warm, humid store air constantly mixes into the air curtain, so the evaporator picks up a lot of moisture and frosts fast. Open multidecks defrost the most often of any case.

Glass-door reach-in (vertical, with doors). Frozen food, ice cream, beverages, increasingly dairy and deli too. Doors cut infiltration dramatically, so the coil stays drier and needs less frequent defrost than an open case at the same temperature. Frozen-food reach-ins run low-temp and use electric (or hot-gas) defrost; the doors usually have anti-sweat (anti-condensation) heaters in the frame and glass.

Coffin / well / "bunker" case (horizontal, open top). Frozen novelties, ice cream, sometimes packaged meat. Cold air pools in the well — cold air sinks, so a horizontal open case actually holds temperature fairly well with relatively little infiltration compared to an open vertical case. Lower frost load, less frequent defrost.

Service / deli / meat case (the "serve-over"). Staffed counters — meat, seafood, deli, bakery, prepared foods. Product sits on a slanted display deck behind glass, with a coil below or behind. Often runs medium-temp; defrost frequency depends on whether it's open-front or glass-front and how much it's loaded with warm product.

Combination cases stack functions: an open produce deck up top with a refrigerated well below, or a multideck with some glass-door sections. Each section may be a separate evaporator circuit with its own TXV and its own defrost.

The case style determines three defrost decisions:

  1. Defrost type. Above-freezing cases (most fresh-product cases) can use off-cycle (warm-air) defrost — just stop cooling and let the case air melt the coil. Below-freezing cases (frozen, ice cream) need electric or hot-gas defrost because the case air is too cold to melt anything.
  2. Defrost frequency. Driven by frost load, which is driven by infiltration. Open vertical multidecks frost fastest → most defrosts per day. Sealed glass-door and horizontal wells frost slower → fewer.
  3. Defrost length and fan handling. Off-cycle just needs the fans to keep blowing case air. Electric/hot-gas needs fans off during defrost and a fan delay afterward so the coil re-cools before fans restart.

In the field

  • Identify the style and the temp class first. Open vs. doored, vertical vs. horizontal, medium vs. low temp. That tells you what defrost type to expect and roughly how often it should run.
  • Find the case's evaporator and defrost gear. Off-cycle (no heaters, fans run through defrost), electric (heaters in the coil + a termination sensor + heated drain on freezers), or hot-gas (a hot-gas solenoid).
  • Read the case controller / defrost schedule. Each case (or lineup) has a defrost count per day and a termination method. Compare it to the case style and the symptom.
  • Check the air curtain and discharge/return on open cases. A disrupted air curtain (blocked honeycomb, fans out, overstocked above the load line, products in the return-air slot) wrecks temperature and piles on frost.
  • Watch a forced defrost to confirm it actually clears the coil and drains, then returns to cooling with the proper fan delay.

Normal values & targets

  • Open multideck (medium temp): product target around the upper 30s°F; defrosts often four or more times a day because of high infiltration. Frequently off-cycle since the box is above freezing.
  • Glass-door frozen reach-in (low temp): product well below 0°F; electric or hot-gas defrost, typically only a couple times a day because doors keep the coil dry. Anti-sweat door heaters run to keep frames/glass clear.
  • Coffin/well freezer: low temp; modest defrost frequency thanks to low infiltration in a horizontal open well.
  • Service deli/meat case: medium temp, product in the mid-to-upper 30s°F; defrost frequency between an open multideck and a doored case depending on construction and load.
  • Discharge air vs. product temp: discharge air off the coil runs colder than the product setpoint; product temperature is what the health inspector and the customer care about — measure product/return, not just discharge.

Representative — always confirm against the case data plate, the controller, and the product being held.

Common faults & what they mean

  • Open case warm on top shelf, cold on bottom — air curtain failure (evaporator fan out, blocked honeycomb, overstocked above the load line). The curtain isn't reaching the top, so the upper shelves lose the cold.
  • Open case frosting/icing fast and not recovering — infiltration too high (defrost frequency too low for the conditions), products blocking the return slot, or a damaged/short-cycling air curtain. More infiltration than defrost can clear.
  • Frozen reach-in doors sweating or icing on the frame — anti-sweat (anti-condensation) heater failure or a control turning them off; glass and frames fog or frost.
  • Any case iced solid — defrost not completing or a frozen/clogged drain refreezing the melt (same root causes as any evaporator: open heater, bad termination sensor, failed hot-gas valve, plugged drain).
  • Product warm but coil looks clean and cooling — not a defrost problem: TXV, EPR setting, solenoid, low charge to that circuit, or a fixture sharing a struggling suction group.
  • Case temp swings with store traffic — open cases are sensitive to ambient store humidity and door-area drafts; heavy traffic and HVAC problems in the store raise infiltration and frost load.

Tech tips & gotchas

  • Case style predicts the problem. Open multidecks live and die by the air curtain and frost load; doored cases live and die by door heaters and gaskets; horizontal wells are the most forgiving. Walk up knowing which fight you're in.
  • Don't blame refrigeration for an air-curtain problem. A warm top shelf on a clean, cooling open case is almost always airflow (fans, honeycomb, overstocking), not charge or metering.
  • Overstocking is a real fault. Product loaded above the load line or stuffed into the return-air slot breaks the air curtain and chokes return airflow. It looks like a refrigeration problem and it's a stocking problem.
  • Off-cycle only works above freezing. If a freezer case got set to off-cycle defrost (no heat), it ices up — wrong defrost type for the temperature class.
  • Anti-sweat heaters are part of a freezer door case. Sweating/frosting glass and frames usually means those heaters (or their control) failed — not the refrigeration.
  • Measure product/return temperature, not just discharge. Discharge air is always colder than product; a case can have cold discharge and still be holding product warm if airflow or defrost is off. Health-code temperatures are product temperatures.
  • Combination cases can have independent circuits. One section warm while the other is fine often means that section's own evaporator/TXV/defrost — check whether they're separate circuits before assuming one fault covers the whole case.

Safety / code notes

  • Product holding temperatures are a food-safety matter under the applicable food code — cold-holding limits drive the case setpoints; document temperatures when servicing.
  • Defrost heaters and anti-sweat heaters are electrical loads — lock out and verify dead before servicing the coil or door circuits.
  • Refrigerant and hot-gas defrost work follows EPA Section 608 — recover, never vent.
  • Condensate drains on freezer cases commonly require heat trace and proper routing per the applicable mechanical/plumbing code to prevent refreezing and pan overflow.