Bohn Evaporator Coils: A 6-Point Inspection Checklist Before Installation

When This Checklist Applies

If you're about to accept delivery of a Bohn evaporator unit, use this checklist before the truck pulls away. It takes about twenty minutes, and it catches the problems that normally surface two weeks later — after the unit is hanging, piped, and loaded with product.

I handle incoming quality review for a distributor that supplies Bohn evaporator coils and commercial refrigeration parts. For the last four years, I've been the person who releases units to contractors. That's roughly 200 units per year, and in our Q1 2024 audit, we logged issues on 33 of 190 deliveries. The most common were the ones you'd expect: model mismatches nobody caught at the receiving dock, transit damage signed off too quickly, and the wrong coil configuration for the room temperature. Almost all of it was preventable.

One caveat before the list: I can only speak to small commercial refrigeration — walk-in coolers, freezers, prep rooms, and similar packaged applications. Industrial ammonia systems and supermarket racks are a different animal, and the rules are different there.

The Six Pre-Install Checks

1. Verify the Bohn evaporator model on the nameplate — not the carton

It sounds obvious, but the carton label and the packing slip are not the unit. The metal nameplate on the evaporator is the only thing that tells you what you actually received. On most Bohn evaporator models, that plate is near the electrical compartment or on the fan plenum. Get close enough to read it clearly.

Compare the model, voltage, phase, refrigerant designation, and defrost type against your purchase order. The suffix matters. Two Bohn evaporator models can share the same cabinet and look identical from the outside while having completely different coils, motors, or defrost configurations inside.

If the paperwork says one model and the nameplate says another, stop. Do not let the installer "make it work." A substitution isn't automatically wrong, but it needs to be a written change order with the price difference visible before installation — not a surprise invoice after the fact. I've learned to ask what's not included before I ask the price. The model number on the quote should be the model number on the unit. Simple.

2. Walk the fin pack before the driver leaves

Open the crate far enough to see the actual coil face — all four sides if you can manage it. Use a flashlight at a low angle across the fins. Crushed or bent sections show up immediately when light reflects off the aluminum.

Some bent fins on Bohn evaporator coils are fixable with a fin comb. It's tedious, but it happens. What you're really looking for is hidden structural damage: fin blocks compressed away from the tubes, tube sheets bent, or copper tubes with dents or deep scratches. A bruised copper tube can pass a static pressure test and then leak six months later when vibration does its work.

If you find damage, write it on the delivery receipt before the driver leaves. Take photos with the bill of lading visible in the frame. I've seen too many freight claims denied because the receiver signed a clean delivery and discovered the problem two days later. "Subject to inspection" on the receipt is not rude. It's basic self-protection.

3. Match the refrigerant and pressure rating to your system

The data tag on a Bohn evaporator lists the refrigerants it's rated for and the maximum working pressure. That tag is not a suggestion. If your system runs a refrigerant that isn't listed on the evaporator tag, that's a stop sign. Don't energize the system until an engineer confirms compatibility.

This matters more than it used to. "Drop-in" refrigerant claims make people comfortable mixing components that were never designed to work together. The operating pressures of a retrofit refrigerant can be higher than the original, and the evaporator coil's pressure rating doesn't change just because someone says the word drop-in.

Also check that the condensing unit or remote condenser selection matches the evaporator's design conditions. An evaporator rated for a low-pressure system won't be happy connected to a condenser that pushes the high side well beyond the coil's rating. If the system was designed as a package, keep it that way. If you're assembling components from different sources, have the application engineer sign off before installation.

4. Count the fins per inch — the check almost everyone skips

Here's the step that separates a good receiving inspection from a paperwork exercise: physically count the fins per inch, or FPI. It takes about five seconds with a flashlight, and it catches problems that no model number check will catch.

Fin spacing is tied to the room temperature. As a rough guide, a cooler coil might be in the 8 to 10 FPI range, while a low-temperature freezer coil is usually wider spaced — often 4 to 6 FPI — because frost builds faster in low-temperature service. More fins mean more heat transfer surface in clean, dry conditions. But in a freezer, dense fins become ice bridges.

Looking back at a 2022 freezer installation, I should have counted fins before releasing the unit. The paperwork said freezer duty. The model tag said freezer duty. Nobody touched the fins. Six weeks after startup, the coil was icing between the rows, airflow dropped, and the system couldn't hold temperature. It turned into a $22,000 redo and delayed the opening. The coil wasn't defective — it was specified for the wrong temperature range. That's exactly the kind of mistake a physical fin check catches on the dock.

5. Verify the defrost components before you hang the unit

If you ordered an electric defrost Bohn evaporator, check the defrost heaters before installation. The heater element has its own rating tag, and it should match the unit voltage. A heater rated at 460 volts connected to a 230-volt supply produces roughly a quarter of its rated wattage, which means slow defrost and endless service calls. The reverse — a lower-voltage heater on a higher-voltage supply — is a safety issue, not a performance issue.

Confirm that the defrost heaters are actually installed. Some units ship with heaters factory-installed; others ship with the heater kit in a separate box. If the kit is separate, confirm it's on the packing list before the installer drives away. Also check the drain pan heater and the defrost termination thermostat. These are the components that make an electric defrost cycle behave predictably.

I'll say one more thing about defrost because it's where I see the worst field workarounds: an infrared heater is not a defrost system. I've watched service technicians point an infrared space heater at an iced coil to "help it along." It melts a stripe across the face of the coil and leaves the core frozen. It can also soften wiring and plastic drain pan components. If the unit's defrost circuit isn't working, fix the circuit. Don't aim a space heater at the problem and call it a day.

6. Check fan rotation and drain pan orientation before rigging

Spin each fan blade by hand before the unit goes up. It should rotate freely without scraping the shroud. If the unit is three-phase, verify the actual rotation direction under power before you mount it — an electrician can do this safely during the pre-install check. Backward fan rotation on a unit cooler is easy to miss at startup and expensive to troubleshoot later.

Then look at the drain pan. Is the drain outlet on the correct side for your installation? Once the evaporator is hanging and the refrigerant lines are run, changing the drain side is a miserable job. Confirm the drain orientation matches the room layout now, while the unit is still on the pallet and easy to swap.

Two Mistakes That Show Up After Installation

The first mistake is ordering replacement parts by category instead of by model. When a customer calls and says "I need a fan for my Bohn," that's not enough. Different Bohn evaporator models use different fan motors, blade diameters, and shaft lengths. The same applies to coils and heaters. If you search online using just the word condenser, you'll get audio tutorials comparing a condenser vs dynamic mic before you get any refrigeration parts. Add the actual Bohn evaporator model number to your search and you'll get components that fit.

The second mistake is treating the price quote as the whole story. I have mixed feelings about how some equipment is quoted. A quote that lists the evaporator at a sharp price but leaves out the defrost kit, drain pan heater, freight, and liftgate will look better on paper and cost more in the end. I'd rather see one number that includes every required option. When you compare quotes, ask what isn't included before you ask for a better price. The vendor who lists everything upfront — even if the total looks higher — usually costs less by the time the unit is running.

The Bottom Line

Twenty minutes on the dock saves a week on the back end. Check the model, check the copper, check the fins, check the refrigerant rating, check the defrost kit, and check the drain before you rig the unit. If something doesn't match, don't sign. Whatever the delivery schedule says, the cost of pulling a wrong evaporator off a ceiling is far higher than the cost of rejecting it on the ground.