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?
The cooler may use off-cycle (air) defrost because the coil can rise above freezing with box air; the freezer needs electric or hot-gas defrost, a heated drain line, and time-initiated, temperature- or time-terminated control with drip time.
Both boxes must use off-cycle defrost because FBC Mechanical bans electric heat in walk-ins.
Both boxes must use hot-gas defrost, and the cooler drain does not need a trap because medium-temperature condensate evaporates.
Freezer fans should run during electric defrost so the box air melts the frost, which is why air defrost also works at 0°F.
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?
An internally equalized TXV, no suction trap, and compressor cycling directly from the box thermostat with liquid sitting in the crankcase is the standard walk-in arrangement.
Use an externally equalized TXV, a suction P-trap at the evaporator with the suction sloped toward the compressor, and a liquid-line solenoid so the compressor pumps down to the low-pressure cutout.
A capillary tube replaces the TXV on any walk-in over 1 ton, and a double suction riser is used only on comfort-cooling air handlers.
Charge a 400-series blend as vapor at the suction service valve until the box thermostat is satisfied; superheat is then automatically correct.
Which statement about walk-in versus reach-in installation and license class is accurate?
A reach-in is any cooler a worker can walk into; walk-ins are always self-contained cabinets with the condenser in the base, and Class B may not install either.
EPRs are illegal on shared-suction racks because every coil must run at the freezer SST, and door heaters are architectural work outside HVAC scope.
A walk-in is a personnel-entry insulated box with a unit cooler; a reach-in is a cabinet the operator does not enter. Class B may install these as separate systems inside the 25-ton cap, but multiple boxes on one 40-ton rack are one system and Class A work.
Safety releases, lighted personnel switches, and freezer pressure-relief ports are optional cosmetics and are not part of the Trade C cooler cluster.
Sections you finish are checked off in the contents.