How a Mitsubishi PLC Quote Taught Me to Ask What's Not Included

The Day the Air Conditioner Died

In June 2024, the control panel for air conditioner unit two stopped working. At 10:30 that morning, our facilities manager sent a text that started with 'we have a problem' and ended with a photo of a panel that looked like a small electric box with a green light that was very much not glowing.

I'm the office administrator for a 40-person company. That means I handle the purchasing that no one else wants: office supplies, print orders, maintenance contracts, and the occasional strange repair. I process maybe 60 to 80 orders a year across 12 or 15 vendors. I report to both operations and finance, so every purchase has to make sense to me and to the spreadsheet.

When I opened the photo from the facilities manager, I saw a name I barely recognized: Mitsubishi FX3S PLC. I'm not an automation engineer. I had to look it up.

That evening, I read Mitsubishi Electric PLC news and product pages instead of watching TV. According to Mitsubishi Electric's product overview (mitsubishielectric.com), the FX3S is a compact PLC designed for small-scale automation. That matched what we needed. Our unit didn't need a giant control system. It needed a small controller that could run a few relays and a thermostat schedule.

The First Quote Was Not the Real Quote

The first vendor said they could replace the control panel for air conditioner for $1,850. They could start Friday. The second vendor quoted $2,300 and listed more details: Mitsubishi PLC module, programming, load testing, commissioning (which, honestly, was the first time I saw those words on a quote). At first, the higher number looked worse. Finance would definitely prefer the lower one.

The most frustrating part was that I couldn't tell whether the two vendors were describing the same job. They both talked about replacing a control panel, but the second one mentioned a program, and the first one didn't mention anything beyond the hardware.

So I asked the first vendor a simple question: what's not included in that $1,850?

The answer changed everything. 'The quote covers the hardware swap if the wiring and program match the existing system.' That 'if' was doing a lot of work. What if the program wasn't backed up? What if the wiring had been modified? What if the PLC needed to be configured from scratch? I didn't know, and that meant the first quote wasn't really a quote. It was a starting point.

From the outside, replacing a control panel for air conditioner looks straightforward. One box out, another box in. The reality is that a PLC is useless without a program. And a program is useless if nobody knows where the backup is. Here's something that never appears on a quote: the assumption.

I also learned that 'commissioning' isn't a fancy word for turning it on. It's the part where someone tests the panel after installation, checks the wiring, and makes sure the inputs and outputs match the program. Without that line item, you're buying a new PLC and hoping it works.

The Programming Problem

I called the facilities manager and asked the same question. He didn't know whether the original program had been saved anywhere. The original installer had long since retired. That made the second vendor's line item for programming not optional. It was the most important part of the job.

I had two working days to make a decision. The office was getting warm, people were complaining, and finance wanted a number. Normally I'd get three quotes and compare them side by side. There was no time for that. I called the second vendor and asked whether they could recover the program from the old PLC if there was no backup.

'Usually, yes, but it depends on the condition of the controller,' they said.

Then they asked for the model number off the old PLC, the power supply voltage, and whether anyone had modified the panel wiring. Those questions told me they'd done this before. The first vendor didn't ask any of that. They just said they could start Friday. Maybe they could. But I couldn't tell if they were replacing a Mitsubishi PLC or just replacing a box.

That was the first honest thing I'd heard all day.

We went with the second vendor. The total was $2,300, about $450 more than the first quote, and the invoice matched the quote to the dollar. The repair took one visit. The AC came back on, and the only emails I got that afternoon were the usual ones, not 'it's still hot.'

There's something satisfying about a repair that goes exactly the way the quote said it would. After my first year of buying things for this office, I'd learned to expect surprises. This time there weren't any.

The Battery Charger Lesson

Now for the battery charger.

A few months ago, I bought a Razor scooter battery charger for my son. The listing said compatible with the scooter, and the voltage matched the old charger. So I ordered it. When it arrived, it worked, but it got hot. That made me nervous. I finally looked up how do you read a battery charger. The answer was on the label the whole time: input voltage, output voltage, output current, and connector polarity. I had matched the voltage but not the current rating.

How do you read a battery charger? You check the label, not the marketing. A charger can say '12V' and still be wrong if the amp rating is too low or too high. The quote for a Mitsubishi PLC works the same way. A number can say 'control panel replacement' and still be wrong if the program, the wiring verification, and the commissioning aren't included.

What I Learned

Look, I'm not saying the lower quote was a scam. It was a quote for a different scope, one that assumed everything would go smoothly. But 'everything goes smoothly' is not a real project plan, and it's not a real price.

What I'd do differently now? I'd ask the same questions on the first call. What's not included? Is programming part of this price? Do you have a copy of the current program? Can you test the new controller before you leave? How do you handle a surprise if the wiring is different? The best vendors answer those questions without getting annoyed.

I've also changed the way I read vendor proposals. I read the assumptions before the total. I look for what's missing, not just what's listed. And I ask for a proper invoice, because finance will reject anything unclear. In 2020, I approved a small order from a vendor who couldn't provide a proper invoice, and I had to redo the whole expense report. I do not need to learn that lesson twice.

So that's my story about air conditioning, a small Mitsubishi PLC, and a battery charger. They don't seem related. They are, though. Every one of them taught me the same thing: the real price is only visible after you understand what's included.