If your prep table is freezing lettuce, proteins, or cut vegetables near the back of the pan rail, the evaporator coil is overcooling that zone. It’s not a sign the unit is working too hard. It’s usually a sign that temperature control has broken down in one specific way. Here’s what’s behind it and what to do.
The Most Likely Culprit: A Stuck or Out-of-Calibration Thermostat
The prep table thermostat (or cold control) tells the compressor when to shut off. When it fails to read the box temperature accurately, the unit keeps running past the setpoint. The air coming off the evaporator is always the coldest air in the cabinet, so whatever sits closest to the coil, usually the back pans, takes the hit first.
A thermostat can fail in two ways: it can stick closed so the compressor never shuts off, or it can read a few degrees low and run longer cycles than it should. The second case is more insidious because the unit still cycles, the display reads normal, and the problem only shows up in the last pan position.
If you have a thermometer probe, put it at the back of the pan rail for 30 minutes. If it reads below 32°F while the display shows 36-38°F, the thermostat or temperature sensor is lying to the controller. That test is yours to run. The actual fix, calibrating or replacing the sensor or cold control, requires a tech with the right tools and parts for your unit.
Airflow Problems
Bad airflow is the second cause, and it’s actually common in prep tables because of how they’re loaded.
The evaporator coil sits at the back of the unit. Cold air is supposed to flow across the pan rail and return through a duct or grill. If pans are overfilled past the pan rail line, full hotel pans are stacked sideways, or the return air path is blocked by a cutting board laid flat across the rail, the airflow circuit breaks. Cold air stalls near the evaporator instead of circulating. Whatever is back there freezes. Whatever is near the front stays too warm.
Check how the pans are loaded. The pan rail depth markers exist for a reason. If pans are riding high or there’s anything blocking the back grill, clear it and give it an hour. That’s a safe check worth doing before anything else. If the freezing continues after you’ve fixed the loading, the problem is mechanical.
Another airflow issue is a dirty evaporator coil. Ice or frost buildup on the coil restricts airflow and changes the temperature distribution inside the cabinet. If you look at the coil through the back panel and see a thick layer of frost, the defrost system may not be working correctly. That’s a technician job.
Door Gaskets and Lid Seals
This one surprises people. A leaking gasket on the lid or front panels lets warm humid air into the cabinet constantly. The evaporator works harder to compensate, the coil gets colder, and the overcooling gets worse near the coil while the rest of the cabinet fights the heat load from the leak.
The quickest check: close the door on a dollar bill and pull it out. If it slides out easily with no resistance, the gasket isn’t sealing. Do that test at several points around the perimeter. Condensation or frost around the door frame is another indicator. If the gasket is failing, a tech can match the correct profile for your unit and replace it as part of the service call.
Refrigerant Overcharge (Call a Tech)
If a technician recently serviced the unit and added refrigerant, and the freezing started shortly after, overcharge is worth mentioning. An overcharged system can cause refrigerant to flood through the evaporator abnormally, leading to icing and erratic temperatures. It’s not something you can diagnose without gauges, and it’s not something you can fix yourself. If this matches your timeline, call the same tech back.
How a Tech Diagnoses This
When we send a technician out for this complaint, the process is straightforward. They’ll check the thermostat calibration against an independent probe, pull gauges to verify the system is running at the right pressures, inspect the defrost timer or adaptive defrost control, and check the evaporator fan motor to make sure airflow is actually moving. On older prep tables with mechanical cold controls, calibration drift is common after a few years. On newer digitally controlled units, a faulty thermistor (the sensor that feeds the controller) is the more common finding.
The repair is usually a thermostat, sensor, or defrost component. Parts availability varies by brand and location, so ask your tech what to expect before the visit. Labor plus parts on a thermostat swap is typically a modest service call; a defrost board or control board costs more. Exact pricing varies by unit and supplier, so get a quote before authorizing work.
What You Can Do Before Calling
Run through this list first:
- Check pan loading depth. Overfilled pans blocking the return air path cause freezing near the evaporator.
- Move a probe thermometer to the back pan position and let it log for 30 minutes. Compare to the display.
- Inspect the door gaskets and lid seals using the dollar-bill test at multiple points around the perimeter.
- Look at the evaporator coil. If it’s covered in frost or ice, note whether the unit normally defrosts (listen for the defrost cycle in the early morning hours).
If the above points to a mechanical or electrical fault, stop there. Running the cabinet warmer to compensate for a broken defrost cycle creates a food safety problem on the other end, and it doesn’t address what’s actually wrong.
When to Call a Pro
If the freezing persists after you’ve ruled out loading and airflow, or if you see ice on the coil, the fix is going to require someone with gauges, a multimeter, and the right parts. In a commercial kitchen, a prep table that’s out of temperature spec in either direction is a health code issue, not just an inconvenience.
We handle prep table repairs across the Bay Area. If you’re in the South Bay, East Bay, or anywhere in the Tri-Valley, reach us through bayarearefrigerationservice.com. We’ll get you on the schedule fast, often same or next day when we can. We’ll diagnose it, tell you what’s wrong, and give you a straight answer on whether it’s worth repairing.