Home › Commercial Refrigeration Guide › Walk-In Cooler & Freezer Guide › Walk-In Evaporator (Unit Cooler) Guide
Updated October 14, 2026
Quick answer
The evaporator, also called the unit cooler, is the fan-and-coil assembly inside the walk-in. It absorbs heat from the box air. Its fan motors, expansion valve, defrost heaters, drain pan and coil are separate parts, so most evaporator problems are repairs, not replacements. Replace the whole unit when the coil leaks or corrodes, or when the refrigerant or system is being changed.
What is inside the evaporator
| Part | Job | Common failure |
|---|---|---|
| Coil (copper tubes, aluminum fins) | Absorbs heat from box air | Leaks from corrosion or vibration; bent or dirty fins |
| Fan motors and blades | Move box air across the coil | Bearings fail; motors burn out; blades crack |
| Expansion valve (TXV or EEV) | Meters refrigerant into the coil | Sticks, loses charge in its sensing bulb, or is set wrong |
| Defrost heaters (freezers) | Melt frost off the coil | Burn out; uneven ice |
| Termination and fan-delay controls | End defrost and restart fans | Fail open or closed |
| Drain pan and heater | Collect and carry away meltwater | Cracks, slime, frozen drain |
Common evaporator problems
- Fans not running
- Coil iced up
- Water on the floor or frozen drain
- A leaking coil, often found as oily spots on fins or a slowly falling charge
- Uneven frost from an expansion valve fault
Repair or replace?
| Situation | Usual answer |
|---|---|
| Failed fan motor, heater, termination thermostat or drain heater | Repair: replace the part |
| Expansion valve fault | Repair: replace or adjust the valve |
| Small accessible leak at a joint | Often repairable by brazing |
| Coil leaking through corroded tubes | Usually replace the evaporator |
| System being converted to a new refrigerant | Depends on the refrigerant and the coil; ask your technician |
| Evaporator undersized after a box change | Replace with a correctly sized unit |
Evaporator replacement means recovering refrigerant, brazing new connections, pressure testing, evacuating and recharging, so it is always a technician job. See repair or replace a walk-in for the bigger picture.
Brands you will find
Walk-in evaporators are made by refrigeration system manufacturers rather than box makers. Common names include Heatcraft's Bohn, Larkin, Chandler and Climate Control lines, Russell, KeepRite and Witt. Many box makers ship systems built around these. See Heatcraft systems, Russell and KeepRite.
Keeping the evaporator healthy
- Keep product at least a foot from the evaporator face and fan guards.
- Have the coil and drain pan cleaned during maintenance.
- Replace shaded-pole fan motors with EC motors when they fail.
- Fix door leaks; they ice the coil.
Expansion valves: TXV vs EEV
| TXV (thermostatic) | EEV (electronic) | |
|---|---|---|
| How it controls | A sensing bulb on the suction line opens or closes the valve mechanically | A controller drives the valve from pressure and temperature sensors |
| Pros | Simple, no power needed | Tighter control, better efficiency, diagnostics |
| Common faults | Lost bulb charge, loose bulb, wrong setting, debris | Sensor or driver faults, wiring |
| Symptoms of failure | Uneven frost, warm box, floodback | Alarms, erratic superheat |
A loose or poorly insulated TXV bulb is a surprisingly common cause of poor cooling. A technician checks superheat before blaming the valve.
Clearances and airflow
Unit coolers need room to breathe. Product stacked against the coil face starves it of air; product in front of the fans gets frozen while the rest of the box warms. Keep at least a foot of clearance in front of the coil, do not store boxes on top of the unit cooler, and keep the area below it clear so the drain pan can be reached. Low-profile units hung near the ceiling are especially easy to block.
Cleaning the evaporator
Evaporator coils collect dust, mold and food particles, especially in produce and prep coolers. A technician cleans them with a coil cleaner safe for food areas, rinses the drain pan and flushes the drain line. Never spray water into fan motors or electrical boxes. Cleaning during maintenance prevents odors, slime and the slow loss of airflow that leads to icing.
Bay Area note
Unit coolers in Bay Area produce, floral and prep coolers collect organic debris that grows mold and slime. More frequent coil and drain pan cleaning keeps them healthy, especially in humid coastal kitchens.
Owner checks
- Are all fans turning?
- Is the coil clear of heavy ice?
- Is the drain pan clear and the floor dry below it?
When to call a technician
Call when fans stop, the coil ices repeatedly, water leaks from the pan, or the box warms while the condensing unit runs.
Open 7 days, 8 AM to 5 PM, with emergency service until 9 PM. CA Lic. #776244.
Frequently asked questions
What is a walk-in unit cooler?
Another name for the evaporator: the fan-and-coil unit mounted inside the box.
How long does a walk-in evaporator last?
Often well over a decade with clean coils and good drainage. Corrosive environments and vibration shorten coil life.
Can an evaporator coil be repaired?
Leaks at accessible joints often can. Leaks inside corroded tubes usually mean replacing the coil or the unit.
Why is my evaporator dripping water?
The drain pan or drain line is blocked, cracked or frozen, or the unit is out of level.
Do evaporator fans run all the time?
On coolers, yes. On freezers, they stop during defrost and for a short delay afterward.
What is superheat?
The amount the refrigerant vapor is warmed above its boiling point at the evaporator outlet; technicians use it to check that the valve is feeding the coil correctly.
How often should the evaporator coil be cleaned?
At each maintenance visit, usually twice a year; more often in produce, floral or dusty boxes.
Why is there mold on my evaporator?
Moisture and organic debris on the coil and drain pan. Regular cleaning and a clear drain prevent it.
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