22.2 Walk-In & Reach-In Coolers
Key Takeaways
- A walk-in is a personnel-entry insulated box with a remote or packaged condensing unit and one or more unit-cooler evaporators; a reach-in is a cabinet the operator does not walk into, often self-contained.
- Medium-temperature coils (box above freezing) may use off-cycle or air defrost; low-temperature coils need electric or hot-gas defrost, a heated drain line, and time-initiated, temperature- or time-terminated control.
- Externally equalized TXVs feed evaporators that have a distributor or a large pressure drop; set superheat from suction-line temperature minus saturated suction temperature at the bulb, not from a box thermostat.
- Suction piping needs a P-trap at a unit cooler hung above the condensing unit, slope toward the compressor, and a double suction riser when part-load velocity will not carry oil up a single riser.
- A liquid-line solenoid and pump-down on the low-pressure control protect the compressor at shutdown; an EPR holds a higher suction at a warmer coil on a shared-suction rack.
22.2 Walk-In & Reach-In Coolers
Trade C’s cooler cluster is the box, not the rooftop. The outline wants walk-in and reach-in installation: evaporators, TXVs, defrost, piping, and controls. Refrigeration & Air Conditioning Technology, 9th Edition (2021) is the book. FBC Mechanical 2023 Chapter 11 still wants listed equipment, machinery-room rules when they apply, and relief that is not dumped into a return-air plenum. Chapter 20 already taught a comfort-cooling line set; this section is a colder evaporator with oil, frost, and a door.
Quick Answer: A walk-in is a room you enter; a reach-in is a cabinet. Medium-temp coils can air-defrost. Low-temp coils need electric or hot-gas defrost and a heated drain. Externally equalize a TXV that has a distributor. P-trap the suction at the unit cooler, pump down on a liquid-line solenoid, and do not set superheat with the box thermostat.
Walk-in versus reach-in
A walk-in cooler or freezer is a personnel-entry insulated enclosure — prefabricated cam-lock panels (walls, ceiling, and usually a floor) or a built-in insulated room — with a unit cooler (forced-air evaporator) on the interior and a condensing unit on the exterior roof, pad, or rack. NSF-listed panels, heated door gaskets, a lighted personnel switch, and a safety release on the door are part of the box, not extras. A reach-in is a merchandiser or worktop the operator does not walk into. Many reach-ins are self-contained (condenser in the cabinet base). Remote reach-in cases on a supermarket rack share a suction header with other evaporators — that is when EPRs and rack controls appear.
Worked box load (teaching scale). A 10×12×8-ft walk-in cooler, 38°F, Florida kitchen, is often in the 1- to 1½-ton neighborhood once infiltration, product pull-down, lights, and wall load are added — not a 5-ton comfort unit “because the kitchen is hot.” Oversizing the condensing unit short-cycles, never pulls humidity, and glazes the coil. Undersizing never recovers after a Monday delivery. Read the box manufacturer’s load sheet and the condensing-unit expanded data at the design SST/SDT (Section 22.1).
Class B may install a 10-ton walk-in plant; Class B may not install a 40-ton rack that happens to feed walk-ins (F.S. 489.105(3)(g) — any one system). Prefabricated walk-in panels are HVAC/refrigeration scope when they complete the refrigeration system; they are not a license to build the restaurant.
Evaporators and TXVs
The unit cooler is a low-temperature evaporator with fans, a drain pan, and (on freezers) defrost heat. Hang it so the air throw covers the box without blowing a gale on product (low-velocity coils for floral, meat, and dough). Keep the coil off the door opening. Condensate must leave through a trapped drain; on a freezer that drain is in a below-freezing room, so it needs heat tape and insulation or the pan ices over and the coil sits in a glacier.
A thermostatic expansion valve (TXV) meters liquid to hold superheat at the coil outlet. Superheat = suction-line temperature at the bulb minus saturated suction temperature from the pressure at that point (Chapter 29 will diagram it; installers still have to set it). Typical medium-temp superheat is on the order of 6–10°F; typical low-temp is often 4–8°F — use the valve manufacturer’s chart, not a 20°F air-conditioning habit. A TXV feeding a distributor (or any evaporator with a large refrigerant-side pressure drop) must be externally equalized: the equalizer tube reads pressure at the bulb location so the valve does not starve the coil. An internally equalized valve on a distributor is a classic glazed-coil, low-suction complaint.
Capillary tubes appear on small self-contained reach-ins; they are not the walk-in answer. Electronic expansion valves on racks still need a pressure transducer and a superheat control — they are not “no superheat.”
Defrost
Frost is water that belonged in the box air. It is a heat-transfer insulator. Medium-temperature coils whose fin surface stays above 32°F most of the cycle can use off-cycle (air) defrost: stop the compressor, leave the evaporator fans running, and let box air melt the frost. That does not work on a 0°F coil — the box air is below freezing.
| Method | Where it belongs | How it is started / stopped | Exam trap |
|---|---|---|---|
| Off-cycle / air | Medium-temp, coil surface above freezing | Box thermostat or timer stops compressor; fans run | Using it on a freezer |
| Electric | Low-temp walk-ins and reach-ins | Time-initiated; time- or temperature-terminated; fans often off during heat | Leaving fans on so you heat the box instead of the coil |
| Hot gas | Racks and some walk-ins | Discharge gas into the evaporator; needs piping and valves | No suction trap, no drain, no termination |
Time-initiated, temperature-terminated is the usual electric-defrost walk-in: a clock starts defrost; a defrost termination thermostat on the coil ends it when the coil is clear, with a fail-safe time so a stuck thermostat cannot cook the box. Drip time (fans delayed after termination) lets water leave the fins before you throw −20°F air across a wet coil and refreeze it as a sheet. Door heaters, pressure-relief ports on freezers, and lighted “person inside” switches are controls on this outline, not kitchen-accessory trivia.
Piping and oil
Suction vapor must carry oil back to the compressor. Velocity in a vertical riser is the oil-return number. A unit cooler hung above the condensing unit gets a P-trap at the evaporator outlet so oil does not sit in the coil during an off cycle, plus a trap or loop at the base of the riser as the manufacturer draws it. Slope horizontal suction toward the compressor. When the compressor unloads or cycles to a low capacity, a single riser may drop below oil-carrying velocity — that is a double suction riser (small riser for low load, both for full load). Insulate the suction to control condensation and superheat gain in a Florida penthouse.
Liquid lines are full-size from the receiver or condenser to the TXV, with a filter-drier and sight glass ahead of the valve. Hot-gas defrost adds a discharge branch, a solenoid, and often a dump tank or suction-header practice from the rack drawing — do not field-invent it. Pressure-test with oxygen-free nitrogen, then evacuate; never use refrigerant as the test gas (Section 22.1).
F.S. 489.105 still fences new building power wiring. The walk-in condensing unit’s dedicated circuit and low-voltage control wiring are HVAC; a new three-phase feeder from the restaurant switchgear is an electrical contractor. Condensate to an existing safe waste, not a direct sanitary tie (FBC 307.2.1.1, Chapter 20).
Controls that belong on the box
A box thermostat (or electronic box control) cycles the liquid-line solenoid. The compressor then pumps down to a low-pressure cutout and stops with the crankcase empty of liquid. Short-cycling on the box thermostat without pump-down is how you slug a compressor after a defrost. A crankcase heater stays on whenever the compressor is off if the manufacturer requires it.
An evaporator pressure regulator (EPR) holds a minimum (higher) pressure — and therefore a higher SST — at a warmer coil that shares a suction header with a colder coil. A crankcase pressure regulator (CPR / holdback) limits the pressure entering the compressor so a hot pull-down does not overload the motor. Oil separators on low-temp racks keep oil in the compressor instead of in −20°F evaporators. Low-pressure, high-pressure, and oil-failure switches are safety, not operating thermostats. Chapter 27 installs the devices; this chapter applies them to the box.
Florida scenario
A certified Class B shop in Pinellas County hangs a 10×12 walk-in cooler (38°F) and an 8×10 walk-in freezer (0°F) for a St. Petersburg restaurant. The cooler unit cooler gets an externally equalized TXV, off-cycle defrost, a trapped drain to an existing safe waste, and a suction P-trap because the condensing unit sits on the pad below. Superheat is set at the bulb, not by turning the box thermostat to 30°F. The freezer gets electric defrost, time-initiated / temperature-terminated with drip time, heat tape on the drain, door heaters, and pump-down on a liquid solenoid. Both condensing units are under 25 tons and are separate circuits, so Class B may contract them. The same drawings show a 30-ton rack in a future phase feeding additional cases — that phase is Class A. Skipping 608 recovery when the old walk-in is cut out is still a federal violation.
Traps: (1) Air-defrosting a freezer. (2) Internally equalized TXV on a distributor. (3) No P-trap on a hung unit cooler. (4) Using the box thermostat as a superheat setting. (5) No drain heat on a freezer. (6) Counting two walk-ins on one rack as two 12-ton “systems” when they share a suction header.
A 0°F walk-in freezer and a 38°F walk-in cooler are being installed in the same Florida kitchen. Which defrost statement is correct?
A unit cooler with a refrigerant distributor is hung on the ceiling of a walk-in, with the condensing unit on a pad below. Which piping and metering combination matches this section?
Which statement about walk-in versus reach-in installation and license class is accurate?