I remember the first time I got called out on a Bohn chiller that kept tripping the breaker. The building engineer was convinced it was a motor issue. The wiring diagram was sitting right there on the control panel cover—clean, labeled, almost too easy to read.
I was six months into my second year in the field (around March 2018), and I was pretty sure I had it figured out. I traced the LRA, checked the contactor, even ran a megger test on the compressor windings. Everything looked fine. So I reset the breaker, slapped the cover back on, and told the customer it was probably just a glitch.
It tripped again 47 minutes later.
Turns out, I didn’t understand what the wiring diagram wasn’t telling me. And that little lesson cost the customer a $1,200 service call plus a spoiled walk-in cooler of dairy products.
The Problem You’re Actually Seeing
When a Bohn chiller trips repeatedly, most techs start with the obvious suspects:
- Overloaded circuit
- Failing start capacitor
- Short-cycling from low refrigerant
- Bad contactor
These are all real possibilities. And the wiring diagram can help you verify each one. But here’s the kicker: the diagram won’t show you why the load is changing in the first place. And that’s usually the root cause.
The Deeper Reason Nobody Talks About
In my experience—and I’ve documented over 30 nuisance trip cases on Bohn equipment—the #1 hidden cause is a gradual voltage imbalance coming from the building’s distribution panel.
I’m not an electrical engineer, so I can’t give you the full harmonic distortion lecture. What I can tell you from a field technician’s perspective is that imbalanced voltage causes the compressor to pull higher current on one leg. That extra current trips the breaker, but it’s not a breaker problem. It’s not a motor problem. It’s a power quality problem.
Honestly, I didn’t believe it myself until I started logging phase-to-phase voltages on every nuisance trip call. In 2019, I caught a 6-volt imbalance on a 208V system. The customer had been replacing breakers every quarter for two years. Nobody thought to check the panel.
The Real Cost of Ignoring This
That 6-volt imbalance was costing the customer more than just breakers:
- Compressor wear accelerated by roughly 40% (estimated based on winding temperature rise)
- Energy consumption increased about 8–10% on that circuit
- Service call frequency: every 3–4 months
When I finally convinced them to have an electrician balance the panel, the chiller ran for 14 months without a single trip. The repair cost: about $400 for a panel rebalance. The previous service call total over two years: over $3,600.
The Simple Fix (That You’ll Want to Add to Your Checklist)
This isn’t complicated. Next time you get a chiller trip call:
- Don’t start with the wiring diagram. Start with a voltmeter at the disconnect.
- Measure L1-L2, L2-L3, and L1-L3 under load.
- If any phase-to-phase reading varies by more than 2%, investigate the upstream panel before touching anything else on the chiller.
- Document the readings. Take a photo. Show the customer.
The wiring diagram is still useful—absolutely. It shows you the intended path of current. But it won’t show you the unintended path of voltage drift.
That’s the kind of lesson you don’t get from a manual. You get it from a $1,200 mistake.
As of December 2024, this checklist has caught 14 voltage imbalance issues in my area alone. The first one saved a grocery store from a weekend shutdown.
