McQuay Equipment FAQ: Water Source Heat Pumps, Fan Coil Manuals, and Thermostat Resets

Hi. I'm the office administrator who handles HVAC service for a 210-person company across two buildings. I've managed maybe 200 service calls since 2020. Maybe 180—I'd have to check the spreadsheet. I'm not an engineer, but I've learned to ask smart questions before calling a vendor. This post covers the McQuay questions I get asked most often, plus a few things I wish someone had told me earlier.

Who actually makes McQuay equipment?

McQuay was a Minneapolis-based HVAC manufacturer with a long history in commercial equipment. Daikin acquired it in 2006, and the North American operation now runs as Daikin Applied. A lot of commercial buildings still have McQuay labels on chillers, water source heat pumps, and fan coil units. That doesn't mean the equipment is obsolete. It means you order parts through Daikin Applied distribution or an authorized distributor. I had to learn this in 2021 when our chiller schedule said McQuay and the local service company told me they couldn't help. They could—they just needed the model number. Look for the data plate, not the brand name on the front. The data plate is usually on the side of the unit or near the electrical panel. Write that number down somewhere safe; you'll need it every time you order a part or request service. According to Daikin Applied (daikinapplied.com, accessed May 2025), McQuay is part of the Daikin Applied brand family.

My McQuay water source heat pump is blowing warm air in cooling mode. What should I check first?

Before you call anyone, check the water loop temperature. Water source heat pumps reject heat into, or absorb heat from, a shared water loop. If that loop is too warm or too cold, the unit will do strange things: blow warm air in cooling mode, short-cycle, or lock out. A mechanical room gage should show loop water somewhere around 60–90°F, depending on season and design. I'm not a technician; I'm telling you the first thing we check after the air filters. A clogged filter can also freeze the coil and confuse the thermostat. We skipped a filter change once (ugh) and paid a $250 diagnostic fee after the unit froze. The filter was the whole issue. Now filter changes are on a calendar reminder, not on the 'whenever someone complains' schedule. I should add that if the unit continues to cycle after checking loop temp and filters, the service tech needs the model number and the alarm code from the thermostat display—that will save time on the first visit.

Where can I find the McQuay fan coil unit manual?

Search Daikin Applied's literature library. The manual is usually a free PDF. You'll need the model number from the data plate on the side of the unit—look for a model string that starts with MCQ or something close to it. I keep a folder called 'B2 Equipment Manuals' and put every manual in it. After our 2024 vendor consolidation project, I had to find manuals for four different fan coil models. It took maybe 30 minutes total once I had the model numbers. What most people don't realize is that the manual isn't just for repair. It shows the recommended filter size, drain pan cleaning interval, and whether the unit can use a standard thermostat. Save it before the service tech leaves. If you can't find the manual online, call Daikin Applied's parts line or a commercial HVAC distributor and give them the model number. In my experience, most distributors will email you the PDF without charging for it. A paid manual download is usually a red flag.

Should I try thermostat replacement before calling an HVAC company?

In many cases, yes. A thermostat is a simple control device. If the McQuay system is otherwise working—no error codes, no unusual noises—replacement can be a 30-minute job. The catch is voltage. Most residential thermostats run on low voltage (24V), but some commercial fan coils and heat pump units use line voltage or special controllers. Check the old thermostat's label and the fan coil manual. If it says 120V or 240V, stop and call a tech. If it's 24V, you can probably match wires to terminals. I replaced two thermostats in our office myself—this was back in 2022—and saved the company around $400 in labor. But I almost ordered the wrong one because I didn't check the heat pump setting. I should add that the replacement has to be configured for heat pump, not conventional, or the system will blow cold air in heating mode. Also write down where each wire goes before you disconnect anything. A label maker helps. This is the kind of task that looks easy until you have two identical wires that do different jobs.

How do I reset a Honeywell thermostat with no reset button?

That phrase confuses a lot of people because most Honeywell thermostats don't have a physical reset button. If the display is frozen or the schedule is wrong, start with the easiest reset: remove the thermostat faceplate from the base, take out the batteries if there are any, wait about two minutes, then put it back. For hardwired thermostats, flip the circuit breaker for 30 seconds. If that doesn't work, use the menu path. Honeywell's support site says the exact path depends on the model—usually System or Advanced Setup, then Factory Reset. As of May 2025, that's still the method shown on Honeywell Home's support pages. Let me rephrase that: before you press any hidden reset, check the model number. I once spent 15 minutes pressing buttons on a Honeywell T4 until I realized the faceplate held the battery and the reset was just removing it. If the thermostat still won't respond after the battery pull and a factory reset, then it's time to think about thermostat replacement. But try the reset first—it costs nothing.

What does a patio heater have to do with McQuay HVAC equipment?

More than you'd think. If your building has McQuay water source heat pumps or fan coils inside, and a patio heater outside, they're both part of the comfort package you're responsible for. The patio heater doesn't connect to the same system, but it belongs on the same maintenance schedule. I started grouping 'comfort equipment' instead of 'HVAC equipment' on our service spreadsheet. That way, the McQuay tech doesn't arrive and tell me the patio heater is out of propane, and the patio supplier doesn't try to sell me a new heater. A lot of buyers focus on the big equipment and completely miss the small stuff: thermostats, fan coil filters, and patio heater burners. Those small failures cost more in emergency visits than preventive checks would. For example, a dirty burner on a patio heater is a safety issue, not just a comfort issue. We now check it in early fall, before the first cold week. If you wait until the week of your holiday party, everyone else is waiting too.

How do I avoid overpaying for McQuay service?

Get the scope in writing before you say go. I ask three questions: what's included, what's NOT included, and how travel and diagnostic fees are billed. A lower hourly rate with a $200 diagnostic fee can cost more than a higher hourly rate with no trip charge. In 2023, I compared quotes for a fan coil valve replacement. One vendor quoted $780; another quoted $950. The $950 vendor included the motorized valve, shipping, and a 12-month labor warranty. The $780 quote covered only the valve cartridge, and the rest added $250. The higher quote was the better deal. Transparency builds trust. If a vendor won't write down what's included, I don't hire them. We've all learned that the hard way. I've started asking about 'time and materials caps' too. It doesn't need to be complicated; I just want a note that says the work won't go above a certain amount without a call. That single line has saved us from surprise invoices more than once.