How to Defrost a Freezer: A Bohn Quality Inspector's Scenario-Based Guide

There's no single answer to "how to defrost a freezer." I know that sounds like a dodge coming from a refrigeration company. But after four years on the quality side of Bohn's commercial line, I've learned the right move depends on the equipment, the frost pattern, and how the unit was serviced before you touched it.

Quick context on who I am: I'm a quality and brand compliance manager for commercial refrigeration products. I review evaporators and condensers before they ship — roughly 30 units a week, maybe 35 when we're pushing seasonal backstock. In 2024 alone I rejected about 2% of first deliveries for issues like a misaligned defrost termination thermostat or a heater wire routed too close to the drain pan. That's not a slap at our production team; it's what quality review is for. And it's why I have a clear view of what fails in the field later.

It took me close to 1,500 inspection reports to understand that most "defective evaporator" returns aren't defective at all. They're the result of a maintenance schedule that didn't exist. So instead of giving you a universal defrosting procedure, let me walk through the scenarios I actually see — and help you figure out which one you're in.

There Are Three Freezer Scenarios (Plus a Bonus)

Every defrost question I get falls into one of these buckets:

• Scenario A — Manual defrost. Your walk-in freezer has no heater in the evaporator. You are the defrost mechanism.
• Scenario B — Electric or hot-gas defrost. Your Bohn walk in cooler evaporator has a defrost timer, a heater, and a termination thermostat. The defrost is automated, but it needs your attention.
• Scenario C — Ice maker freeze-up. The thing that's frozen is a Frigidaire ice maker (or similar). That's a harvesting problem, not a defrost problem.
• Scenario D — Heat-exchange equipment that isn't a freezer. This one catches people off guard. Stick with me; it'll make sense.

The cheap fix in one scenario can be the expensive mistake in another. That's why the one-size-fits-all advice you see online — "turn it off and leave the door open" — doesn't cut it for commercial equipment.

Scenario A: Manual Defrost on a Walk-In Freezer

If your evaporator has no heater pads and no defrost timer, you're in manual defrost territory. This is typical on smaller walk-ins — under 400 square feet or so — and on some older Bohn refrigeration products that are still running strong after 20 years.

The classic mistake in this setup is chipping ice off the coil with a screwdriver. I understand the temptation: the frost is a quarter-inch thick, the drill is right there, and the freezer is full of product that needs to stay cold. But a screwdriver through the coil is not a defrost; it's a $1,000 repair. Or rather, $1,200 after you add the EPA Section 608-certified technician, the refrigerant, and the lost product. I've reviewed return photos of coils punctured exactly that way. The photos don't get easier to look at.

The actual process is boring, and that's a feature:

1. Move product to a backup freezer or consolidate it under insulated blankets.
2. Switch off the unit or trip the circuit breaker.
3. Let the ice melt with the door open. Use a floor fan to move air — never a hammer, never a scraper.
4. When the bulk of the ice is gone, wash the coil with lukewarm water (keep it under 110°F to avoid thermal shock).
5. Clean the drain pan and the floor drain before you close the door and restart.

The prevention part matters more than the procedure. If you're manually defrosting more than once a month, something upstream is wrong — the door gasket, the floor drain heater, or a fan motor on its way out. I'm not 100% sure why the drain heater gets skipped so often in walk-in inspections, but it's the first thing I look for in a freeze-up claim. Take five minutes to check those before you invest in a full service call.

Scenario B: Electric Defrost on a Bohn Walk-In Cold Room

Most Bohn walk in cooler and freezer units use electric defrost. A timer accumulates compressor run time and kicks off a heater cycle every 4 to 6 hours; a termination thermostat ends the heat when the coil surface reaches about 55°F. In principle, you never touch it. In practice, three parts deserve attention.

The time clock. It tracks compressor hours, not wall-clock hours. A 4-hour interval on a unit that runs half the time means one defrost every 8 hours of real time. That's usually fine enough — just understand what the clock is counting.

The heater routing. The heater needs to be evenly distributed across the finned coil, with extra attention near the drain pan. When we see a unit returned for "ice left in the corners of the drain pan," the heater is often bunched near the center. Ask your service tech for a photo next time they open the access panel. If the heater is touching the drain pan itself instead of the fins, that's a scraping noise and a melted pan waiting to happen.

The termination thermostat. This is the most underrated safety part on the evaporator. If it fails closed, the heater stays on past the melt and can overheat the coil. If it fails open, the heater runs until the fail-safe timer cuts it off — and the frost might not melt fully. In my experience, maybe 1% of first-unit thermostats are out of calibration; that's why we test every batch at the factory, and why I'd never approve a "defrost reset" without checking the sensor too.

In my first year reviewing this product line, I made the classic mistake of trusting the supplier's calibration certificate instead of testing a sample batch myself. We shipped a run of evaporators, and two of them came back with blistered heater tubes because the thermostat sensor wasn't strapped to the coil. Cost us a customer, roughly $4,000 in freight and labor, and a very quiet room in a weekly review meeting. Now every batch gets a thermostat check on the bench.

ASHRAE's refrigeration handbook lists three standard defrost methods — off-cycle, electric, and hot-gas — and the fundamentals haven't changed in decades: the heater melts, the thermostat ends it, the drain drains. When that sequence fails, it's rarely the heater. Usually it's the thermostat, or airflow across the coil that's so weak the frost keeps up with the melt.

Scenario C: When It's Actually a Frigidaire Ice Maker, Not a Freezer

Here's a conversation I have way too often: a restaurant calls in, says the "freezer is frosting up," and it turns out the real problem is a Frigidaire ice maker in the corner. They googled "how to defrost a freezer," got a walk-in procedure, and turned off the ice maker for a day for nothing.

An ice maker is a harvester, not a freezer. Water freezes against a grid plate, then a harvest cycle heats the plate just enough to release the cubes. When that cycle doesn't complete, you get thin cubes, slushy ice, or a solid block formed around the evaporator grid. It looks like a defrost failure. It's usually a hygiene and airflow problem instead.

On the Frigidaire air-cooled ice makers we see most often in commercial kitchens, the condenser coil collects grease and flour dust in a way that a walk-in freezer coil never does. That raises the head pressure, the harvest valve opens late or not at all, and the unit refreezes around the grid. A condenser brush and a 15-minute cleanup will fix more of those calls than any defrost setting will.

Also: never use a metal scraper on the grid. I'll say it more directly — stop it. The grid is plated for release. Scrape it once, and cubes will stick to that nick for the rest of the unit's life. Run a sanitizing and cleaning cycle per the manufacturer's schedule instead.

Scenario D: The Heat-Exchange Lesson from a Patio Heater

Let me finally explain the patio heater reference. It's not random.

Every piece of Bohn refrigeration products follows the same physics: heat or refrigerant moves through a coil, and air moving across that coil decides how well the equipment works. A frosted evaporator is a blocked heat exchanger. But a dusty condenser, a lint-covered ice machine coil, and a sooted patio heater emitter are also blocked heat exchangers.

I noticed this while reviewing seasonal equipment late last year. A customer swore his patio heater was failing — "new unit, orange flame, not hot enough." First warm day, same unit worked fine. It wasn't a mysterious electronics problem. The emitter screen had caked on a half-season of dust and cooking residue, and once the airflow cleared, the heat output came back.

The lesson I keep repeating: before you replace the equipment, inspect the air path. That applies to a Bohn walk in cooler in July and a patio heater in September. Same science, similar maintenance. If you're about to tear down an evaporator, pause, feel for airflow across the coil first, and check the filter or the fin spacing. Clean the exchange surface before you touch the refrigeration circuit.

How to Identify Your Scenario in Two Minutes

Let's skip the "use your judgment" endings and give you a usable test.

Step 1 — Look for heater wires on the evaporator. If you see metal-sheathed heater loops running through the fins, you're in Scenario B. If there's nothing but fins and refrigerant lines, Scenario A.

Step 2 — Check what actually froze. If your unit makes ice cubes and the complaint is thin cubes or a block on the grid, you're in Scenario C. A walk-in freezer doesn't make cubes; an ice maker does.

Step 3 — Ask when the problem appears. Does the trouble show up after a season change or after the equipment sat idle? That's Scenario D — inspect the air path, the filter, and the exchange surface before you schedule deeper repairs.

If you answer "multiple scenarios at once," start with B. A walk-in electric defrost system is the most common, the most standardized, and the easiest to verify. From there, you can rule things out in 10 minutes without opening the refrigerant circuit.

Here's my closing thought from the quality side: five minutes of inspection beats five days of correction. That's not a slogan — I've seen an $18,000 replacement order placed for a failure that turned out to be a $40 termination thermostat and a dirty filter. We shipped the replacement anyway, because the customer was demanding it, but it didn't need to happen.

The equipment did what it was designed to do. The maintenance schedule just didn't exist.

Whatever scenario you're in — manual defrost, electric defrost, an ice maker, or seasonal heat-exchange equipment — start there. Know the equipment, verify the air path, and keep the exchange surfaces clean. That's the most practical way to defrost a freezer, and the cheapest way to keep it from freezing up again.