5-Step McQuay Chiller Tech Support & Air Filter Replacement Checklist

This checklist is for anyone who manages a commercial building's HVAC system—specifically McQuay chillers, heat pumps, or fan coil units. Maybe you're the office administrator who got handed the maintenance log. Or the facilities person who needs to solve a 'unit not cooling' call before the VP notices. Either way, this is the playbook I wish I'd had when I took over purchasing and maintenance for our 400-person office back in 2020. Five steps, from finding the model number to getting the right support. Let's go.

Step 1: Locate the Model & Serial Number Before You Touch Anything

This sounds obvious, but you'd be surprised how many support calls start with, 'Uh, it's the big blue one.' McQuay chillers and heat pumps have a manufacturer's nameplate—usually on the side of the control panel or near the compressor access door. It'll list the model number, serial number, and refrigerant type.

Take a photo with your phone. I keep a folder called 'HVAC specs' on mine. Saves a ton of time when you're on hold with tech support and they ask for the serial. In our building, the chiller model was a McQuay WMC series, and the serial was stamped right below the barcode. Without that photo, I'd be reading off a blurry label with a flashlight.

What if the nameplate is worn or missing?

Check the controller interface—on newer McQuay units (post-2010), you can often pull the model info from the MicroTech II or III controller menu. Look for a 'System Info' or 'Unit Data' screen. If that's not an option, contact your local McQuay parts distributor. They can sometimes narrow it down by the unit's physical dimensions and compressor type.

Step 2: Get the Right Technical Documentation

Once you have the model number, go to the McQuay (now Daikin Applied) website or call their tech support line. Ask for the Installation, Operation, and Maintenance (IOM) manual and the service manual for your specific model. These are not the same thing. The IOM tells you how to run it; the service manual tells you how to fix it.

I made the mistake of downloading just the IOM for our WMC chiller. Took me an hour of reading before I realized it didn't have the troubleshooting flowchart. Had to call back and ask for the service manual specifically. Looking back, I should have specified that upfront. At the time, I thought 'manual' meant everything. It doesn't.

Pro tip for model-specific searches:

Use Google with quotes: "McQuay WMC 150 service manual" or "McQuay WMC IOM PDF." If you can't find a direct PDF, try the Daikin Applied parts portal (daikinapplied.com). Most McQuay legacy manuals are archived there. As of January 2025, the site still has manuals going back to the early 2000s.

Step 3: Basic Troubleshooting Before You Call Tech Support

Before you dial tech support, check these three things. You'll save yourself a 30-minute hold time—and maybe a service call.

1. Is the unit powered on? Sounds dumb, but I've had a maintenance guy flip the wrong breaker. Check the disconnect switch near the unit and the control transformer fuse.
2. Is the water flow established? For water-cooled chillers, a no-flow condition will trip the safety. Check the pump status and the flow switch.
3. What's the alarm code? Look at the controller display. Write down the exact code. When you call tech support, they'll ask for it. Saying 'flashing red light' is not a code.

The most frustrating part of chiller troubleshooting: the same issues keep recurring despite clear communication. You'd think written specs would prevent misunderstandings, but interpretation varies wildly. For our unit, the 'low evaporator pressure' alarm was actually a dirty water filter—not a refrigerant leak. I learned that after the third service call.

Step 4: Air Filter Replacement – The One Thing You Can Do Yourself

Air filter replacement for McQuay fan coil units and air handlers is probably the highest-impact, lowest-effort maintenance task you can do. And it's the most commonly ignored. Here's the checklist:

1. Turn off the unit. At the disconnect switch. Not just the thermostat. I've had filters blow back into the coil because the fan started mid-change.
2. Measure the old filter. Don't trust the nominal size printed on the frame. Actual size matters. McQuay fan coil units often use non-standard sizes. Write down the actual dimensions (length x width x thickness).
3. Buy the right MERV rating. Too high (MERV 13+) and you'll restrict airflow, causing the coil to freeze or the motor to overheat. Too low (MERV 4) and you're not filtering anything. For most commercial McQuay FCUs, MERV 8 is the sweet spot. Check your unit's manual for the max allowable MERV—it's usually listed in the 'filter specifications' section.
4. Insert the new filter with the airflow arrow pointing into the unit. I bought the wrong ones once—reversed the arrow. Unit ran fine for a week, then started freezing. The filter was collapsing inward.
5. Reset the filter timer (if applicable). Some McQuay controllers have a filter maintenance reminder. After replacing, go into the menu and reset it. Otherwise, you'll get a 'Check Filter' alarm every morning at 6 AM.

Prices on filters vary wildly. As of January 2025, a standard 20x20x2 MERV 8 filter runs about $6-12 from major online suppliers. You can verify current pricing at Grainger or Uline. But don't buy the cheapest—they often have lower pleat count and higher pressure drop. I found that out the hard way.

Step 5: When to Call McQuay Tech Support – And How to Make It Fast

You've done steps 1-4. The alarm code is still there. The unit still won't start. It's time to call McQuay (Daikin Applied) Tech Support. Their number is on their website—look for the 'Technical Support' page. Expect a hold time of 5-15 minutes during business hours. Have your model, serial, and alarm code ready. That will get you to the front of the queue.

Here's what tech support will likely ask:

• Model and serial number (you have that, right?)
• Alarm code (you wrote it down?)
• Refrigerant type and pressures (they'll walk you through reading the gauges)
• Controller model and display status

So glad I put all this info in a binder near the unit. Almost didn't—would have wasted 20 minutes running back to my desk to look it up. Dodged a bullet there.

What if you don't get a quick answer?

After the third or fourth time the same issue pops up, I was ready to give up on the phone support entirely. What finally helped was building a relationship with a local McQuay service provider. They know the specific quirks of the units in your region—like how our Boston office chiller handles the cold-start sequence in February. Tech support can tell you the theory. A local tech can tell you the reality.

Common Mistakes to Avoid

After managing HVAC maintenance for 5 years, these are the three most common errors I see (and made myself):

1. Assuming the manual covers your exact unit. McQuay has made dozens of revisions to the same model. A 2015 WMC chiller is not identical to a 2020 WMC. Always verify the manual version matches your unit's serial range.
2. Skipping the filter replacement schedule. 'It looks clean' is a trap. A clean-looking filter can still be clogged with fine dust. Stick to the 3-month schedule for fan coil units in an office environment. For a chiller with a condenser coil, that's an annual clean—but check it quarterly.
3. Not documenting what you did. Keep a log. Date, model, serial, alarm code, action taken, outcome. When the same alarm returns in 6 months, you'll have a history. The vendor who couldn't provide proper invoicing cost us $2,400 in rejected expenses. The lack of maintenance logs cost us a $1,200 service call for a problem I fixed myself the year before.

Bottom line: most chiller issues are either power, water flow, or filter-related. The rest is what tech support is for. But with this checklist, you'll handle the easy stuff yourself—and be prepared for the hard stuff when it comes.