I’m a service coordinator at a mid-sized refrigeration company. I’ve handled about 300 service calls in the last five years—from small restaurant walk-ins to massive industrial cold storage. And I can tell you: one of the most common calls we get is about Bohn evaporator coils freezing up.
When a coil freezes, the first thing people do is grab a space heater, a Dewalt fan, or—if they’re really desperate—a heat gun. That works for about an hour. Then the ice comes back. I know because I’ve done it myself. But here’s the thing: you can melt ice a hundred times, but if you don’t fix the root cause, you’re just wasting time and electricity.
The Surface Problem: Ice on the Coil
If you’re reading this, you’ve probably seen it: a Bohn evaporator coil that looks like a block of ice. Thick frost, reduced airflow, maybe even water dripping down the side. The immediate thought is, “The coil is bad. I need a new one.”
But here’s what I learned the hard way: in about 80% of the cases I’ve dealt with, the coil was fine. The ice was a symptom, not the disease.
A Bohn evaporator coil is designed to pull heat out of the air and transfer it to the refrigerant. When it works right, the coil stays at a temperature slightly above freezing. When it stops working right, the coil drops below freezing, and moisture in the air turns to ice instead of water. Cue the space heater.
So what’s causing the coil to get too cold? That’s the deeper question.
The Deeper Cause: It’s Not the Coil, It’s the Heat Pump (and Airflow)
I wish I had tracked this more carefully over the years. What I can say anecdotally is that in about 70% of coil freeze cases I’ve seen, the problem was one of two things: a heat pump issue or an airflow issue.
Let’s start with heat pumps. If your system uses a heat pump, the defrost cycle is critical. Most heat pumps have a built-in defrost cycle that runs periodically to melt ice off the coil. But if the heat pump’s defrost sensor fails—or if the system is set up wrong—the defrost cycle won’t run when it should. The ice builds up, and you’re left with a frozen coil.
I’ve seen this happen in April 2024 at a grocery store. Their Bohn coil was encased in ice. The technician had already been called twice to clean it. The store manager was about to order a new coil. But when we tested the heat pump, the defrost sensor was reading -10°F even though the ambient was 35°F. The sensor was broken. Total fix cost: $85 for a sensor. The new coil they almost ordered: $2,200.
Now, airflow. A Bohn evaporator coil needs a certain amount of air moving across it. If the airflow is restricted—by a dirty filter, a blocked intake, or even a Dewalt fan pointed at it wrong—the coil can get too cold. Less air means less heat to absorb, which means the refrigerant gets colder, which means more ice.
I once got a call from a restaurant that had been fighting a frozen coil for a month. They had tried a space heater, a fan, everything. I walked in and saw the filter: it was covered in a layer of grease so thick I could barely see through it. Replaced the filter, cleared the intake. Ice gone in hours. They had spent $400 on heat guns and lost a lot of sleep over a $12 filter.
The Real Cost: Time, Lost Product, and Stupid Decisions
Let me be honest: when you’re facing a frozen Bohn coil, you’re not just dealing with ice. You’re dealing with consequences.
Time is the biggest one. Every hour the coil is frozen means less cooling. If you’re storing food, that’s a health risk. If you’re storing product, that’s spoilage. I’ve seen a restaurant lose $3,000 of inventory in one day because their walk-in freezer was creeping toward 50°F.
Then there’s the cost of temporary fixes. A decent space heater runs about $50. A Dewalt fan is another $80. A heat gun is $40. Over a few months, you can easily spend $300 on things that don’t solve the problem. Meanwhile, the root issue gets worse.
And then there’s the decision-making under pressure. I’ll be honest: I’ve made some bad calls in the heat of the moment. In February 2023, I approved a rush order for a new Bohn coil without double-checking the heat pump. We paid $300 in rush fees, got the coil in 48 hours, swapped it, and the new one froze too. That’s when I finally checked the defrost sensor. I learned that day: check the simple things first.
The Solution (Short Version)
Look, I’m not going to pretend I have all the answers. But from my experience, here’s what actually works when your Bohn evaporator coil freezes:
1. Check airflow first. Clean or replace the filter. Make sure nothing is blocking the intake. Feel the air moving across the coil. If it’s weak, that’s your problem.
2. Check the defrost cycle. If you have a heat pump, verify that the defrost sensor is functioning. You can test it with a multimeter or call a technician who knows Bohn specs.
3. Don’t rush to replace the coil. In most cases, the coil is fine. The problem is the system around it. A new coil with the same airflow or defrost issue will freeze just as fast.
I don’t have hard data on industry-wide coil replacement rates. But based on my 300+ service calls, I’d estimate that 8 out of 10 frozen Bohn coils are fixed without replacing the coil. The ones that do need replacement are usually damaged from repeated freezing—cracked fins or ruptured tubes.
If you’re facing a frozen coil, take a breath. Don’t grab a space heater yet. Check the basics. Nine times out of ten, the fix is simpler than you think.
And if you’re still stuck? Call someone who’s seen a few hundred of these. We’ve got your back.
