Why I'm Writing This
I'm a commercial HVAC technician handling McQuay system maintenance orders for about 8 years now. I've personally made (and documented) 12 significant mistakes, totaling roughly $23,000 in wasted budget. Now I maintain our team's checklist to prevent others from repeating my errors.
This isn't a textbook. This is what I wish someone had told me before I started working on McQuay equipment. Specifically, the fan coil units (FCUs). Because that's where most of my screw-ups happened.
What We'll Cover
Think of this as a FAQ for avoiding the dumb stuff. We'll hit:
- The #1 McQuay FCU manual mistake. I made it on a 47-unit order.
- Why cheap 16x20x1 air filters cost me $3,200.
- Can an infrared heater really help? Or is it hype?
- And what about that Can-Am air filter upgrade I keep hearing about?
Question 1: What's the biggest mistake you see with McQuay FCU maintenance?
Hands down: ignoring the fan coil unit manual.
I know, I know. It sounds boring. But in September 2022, I had a 47-piece order—all McQuay FCU units—and I didn't check the manual for the specific model's fan speed settings. I assumed 'high speed' was the same across models. It wasn't.
The result? 47 units installed with the wrong static pressure setting. They sounded like jet engines. Every single one had to be re-visited. That cost me $890 in redo labor plus a 1-week delay on the project schedule. My boss was not happy.
The lesson: Always pull the PDF for that specific model. The McQuay fan coil unit manual isn't just paperwork. It tells you the exact CFM range, motor amp draw, and static pressure limits. Ignore it at your own risk.
Question 2: Is it really that important to change the 16x20x1 air filter regularly on these units?
Short answer: Yes. Longer, more painful answer: I learned this the hard way.
I once had a maintenance contract for a small office building with 8 McQuay FCUs. The client asked if they could save money by using cheaper, non-standard 16x20x1 air filters. I said sure—big mistake.
We swapped to a budget filter that was actually a 16x20x1, but it wasn't a MERV 8 like the manual specified. It was a MERV 4. The units ran fine for about 6 months. Then the coils started freezing up in the summer. Then the condensate pans overflowed.
I won't bore you with the details, but that $200 savings on filters turned into a $3,200 problem when we had to pull and clean two coil assemblies and replace a blower motor on the third unit. The motor died because it was working too hard against a partially clogged coil.
My take: A 16x20x1 air filter at MERV 8 costs maybe $5-8 each. The cheap ones are $2. But if it causes a blower motor failure, you're looking at a $800+ repair. Do the math.
Question 3: I heard you can use an infrared heater for defrosting coils on McQuay units. Is that a real thing?
Yes, but proceed with caution. I'm not a refrigeration specialist, so I can't speak to the thermodynamic design of the system. What I can tell you from a maintenance perspective is that infrared heaters are sometimes used for localized freeze protection in outdoor air handling units or mechanical rooms where ambient temps drop too low for the unit's standard operation.
Here's where I messed up: a client had a McQuay AHU in an unconditioned attic. They wanted to add an infrared heater to prevent the coil from freezing. I selected an infrared heater based on the square footage of the room, not the specific CFM of the unit. The heater was too small. It didn't prevent the freeze-up.
Cost of the mistake: two failed DX coils at about $1,100 each, plus the labor and refrigerant. So, my advice? If you're adding an infrared heater for freeze protection, get the manufacturer's spec. Don't guess. And consider if a thermostat-controlled electric heater or a steam preheat coil might be a better solution for your specific setup.
Question 4: What about Can-Am air filters? Are they just for off-road vehicles, or can you use them on HVAC?
Interesting question! This gets into a specialty area. Can-Am is a brand that's famous for their high-performance air filters used in racing and off-road vehicles (like dirt bikes and ATVs). They are NOT standard HVAC filters.
Someone once asked me if they could retrofit a Can-Am air filter onto the intake of their commercial McQuay unit to improve filtration. That's a no-go from a safety and performance standpoint. Can-Am filters are designed for high-velocity, dirty environments. They are often oiled foam or cotton gauze. They do not meet UL 900 or ASHRAE 52.2 standards required for commercial HVAC systems.
My experience is based on about 200 commercial HVAC service orders. I can't speak to how a Can-Am filter might work in a sealed system with a cooling coil. I can tell you this: if you install one without verifying the specs, you risk voiding your equipment warranty, increasing fire risk, or causing static pressure issues that kill the blower motor.
Stick with the manufacturer-recommended replacement filters for the McQuay unit. If you want better filtration, talk to a factory rep about upgrading the filter rack to accept a higher MERV-rated panel. Don't jury-rig a Can-Am filter.
Question 5: So, what's your final tip for someone maintaining McQuay units?
Stop guessing. Read the manual.
This sounds like advice from a guy who talks down to people. But I'm saying it as someone who lost $3,200 on that 47-unit FCU order because I didn't check the McQuay fan coil unit manual for the specific static pressure setting.
Here's my checklist I give to every new technician on the team:
- Model number: Write it down. Not just 'McQuay FCU'.
- Manual: Find it. It's usually a PDF on the manufacturer's website.
- Filter spec: Confirm the size (16x20x1? 20x25x4?) AND the MERV rating.
- Supply voltage: Check the nameplate. Not the breaker.
- Thermostat compatibility: Don't assume a new thermostat will work with an old board.
That checklist has saved me from 4 potential disasters in the past year. It's not fancy. It's effective.
Pricing note: As of January 2025, a replacement McQuay FCU motor (OEM) runs about $400-600. A generic 16x20x1 MERV 8 filter is about $8-12 at a supply house. A proper McQuay fan coil unit manual PDF is free on their site. The cost of ignorance? Much higher.
