McQuay Water Cooled Chiller Maintenance: Evaporator Coil Cleaning, Cooling Fan Checks, and a Winter Propane Heater Warning

I’m a quality manager at a commercial HVAC service company. I review every maintenance report before it goes to the customer—roughly 200 reports a year. In 2024, I rejected about 12% of first-run reports, mostly for missing baseline readings or coil work that couldn’t be verified. This guide is the six-step checklist I wish every technician followed on McQuay HVAC maintenance.

It applies to two situations: a McQuay water cooled chiller with a shell-and-tube evaporator, and finned evaporator coils in air handling units and fan coils. If you’re dealing with either, follow this order:

1. Identify the coil type before you touch anything.
2. Record baseline data.
3. Clean the evaporator coil the right way.
4. Check the cooling fan.
5. Handle cold-weather heating safely.
6. Sign off with measurable proof.

Step 1: Identify the actual evaporator coil type

Here’s the part that trips up a lot of maintenance requests: “evaporator coil” does not mean the same thing on every McQuay system.

On a McQuay water cooled chiller, the evaporator is a shell-and-tube heat exchanger. The water flows through the tubes, so cleaning the evaporator means cleaning the water side, not spraying refrigerant-side surfaces. On an AHU or fan coil, the evaporator coil is a finned air-side coil, and cleaning means rinsing dirt off the fins and tubes. Mixing those two methods is how expensive mistakes happen.

That’s the first check. Know which one you’re standing in front of.

Step 2: Record baseline data before cleaning

If you don’t have numbers from before cleaning, you can’t prove cleaning helped.

For a chiller, record:

• Entering and leaving chilled water temperatures
• Water flow rate
• Evaporator pressure drop
• Refrigerant pressures and superheat
• Compressor amps

For a finned air-side coil, record static pressure across the coil and supply air temperature before and after.

In 2022, I put a standard report template in front of every technician at our company. The first year, about 30% of reports still came back without a baseline pressure drop. We started rejecting those reports until the numbers were filled in. It sounds like paperwork, but it catches real problems. If the pressure drop is already high before you clean, the coil was fouled. If it stays high after cleaning, you have a blockage or a flow issue.

Step 3: Clean the evaporator coil the right way

Now the main event: here is how to clean evaporator coil tubes on a McQuay water cooled chiller, and then the finned-coil version for air handlers.

Water-cooled chiller evaporators

For a McQuay water cooled chiller, the evaporator tubes need mechanical cleaning when fouled. Here’s the sequence:

1. Isolate and drain the chilled water loop.
2. Remove the water heads.
3. Inspect the tube bundle for scale, sludge, and debris.
4. Brush each tube mechanically with an appropriate tube brush.
5. Flush the bundle until the water runs clear.
6. Replace gaskets and torque the water heads to the manufacturer’s spec.
7. Refill, vent air, and re-check strainers.

I went back and forth on a 2023 job between chemical cleaning and pulling the tubes for brushing. Chemical cleaning was cheaper and faster. My gut said the bundle was worse than the pressure drop suggested. It turned out the tubes were packed with mud—not just scale. We brushed every tube and flushed for half a day. The evaporator delta T came back, but only after the mechanical cleaning, not before it.

One more thing: if the work involves opening the refrigerant side of the chiller, the technician needs an EPA Section 608 certification. Water-side cleaning does not require it, but refrigerant recovery and recharging absolutely does.

Finned evaporator coils in AHUs and fan coils

For the finned coils, skip the pressure washer. High-pressure water flattens fins, drives dirt deeper, and can bend the aluminum. That kills airflow.

1. Lock out power to the fan and unit.
2. Remove and inspect filters. Replace them if they’re dirty.
3. Straighten bent fins with a fin comb where needed.
4. Apply a pH-balanced coil cleaner and let it soak for the time on the label.
5. Rinse with low-pressure water (under 400 psi) from the discharge side toward the entering side.
6. Check the condensate drain and pan. Clear any blockage.
7. Let the coil dry, then run the fan for 10–15 minutes before reinstalling filters and panels.

That last step—running the fan dry—is the one everyone skips. A wet coil collects dust immediately. Five minutes of fan time saves the next cleaning from being needed sooner. It’s boring. It works.

Step 4: Check the cooling fan

Cooling fans move enough air to make or break a system. On McQuay HVAC maintenance, that includes condenser fans, air handler fans, and cooling tower fans.

For each cooling fan:

• Check blade tip clearance and look for cracks or missing counterweights.
• Inspect belts for wear and proper tension.
• Lubricate bearings if the motor requires it.
• Measure motor amps and compare them to the nameplate rating.
• Take a motor housing temperature reading with an infrared thermometer.
• Verify rotation direction. A three-phase fan wired backwards runs, but it moves very little air.

During our 2024 startup season, we caught two fans running in reverse on separate jobs. They sounded fine. Amp readings were low. The airflow was maybe 40% of design. Rotation checks are the cheapest fix I know.

Step 5: Use propane heaters safely during cold-weather service

Now the one that worries me every winter. If you’re tempted to run a propane heater in a mechanical room to keep warm while you work on a McQuay water cooled chiller, stop and think first.

Propane combustion produces carbon monoxide and a lot of water vapor. That water vapor settles on electrical panels, motor windings, and coils, and it accelerates corrosion. I’ve seen the aftermath on a $22,000 redo at a medical office building—it wasn’t the heater itself; it was the moisture and CO from a ventless heater running all night during a shutdown. (This was back in 2023, and we changed the winter work rules because of it.)

If you absolutely must use a propane heater in a cold shop or mechanical space:

• Place it at least 10 feet from the chiller, panels, and any plastic drain pans.
• Point the heat away from evaporator coils and electrical gear.
• Ventilate the space. Open a door or use forced ventilation.
• Run a carbon monoxide monitor while anyone is working.
• Never leave it running unattended.

Better yet, use an electric fan heater. If you need to keep a chiller room warm enough to prevent freeze-up, a properly sized electric heater or the building’s own heating system is the safer choice.

Step 6: Sign off with measurable proof

This is my part. I don’t sign a maintenance report that just says “coil cleaned.” I need the before and after numbers, the photos, and the checklist.

For a water cooled chiller, the proof is evaporator pressure drop and delta T returning to expected range. For a finned coil, it’s static pressure drop across the coil and visual confirmation. If the numbers are still off, the work isn’t done.

Also, don’t oversell the result. I once rejected a report that said “cleaned coil to save 30% energy.” That’s an energy-savings claim, and under the FTC’s Green Guides, it needs substantiation. Unless you have field test data for that exact system, say what you can prove: “restored rated heat transfer and airflow.” That’s still a good outcome.

If the chiller oil analysis is part of your maintenance plan, mail the sample in a sealed, leak-proof container with absorbent material around it. USPS has packaging rules for diagnostic specimens, so check the current rules before you ship.

Common mistakes to avoid

• Pressure washing a finned coil and flattening half the fins.
• Cleaning a chiller evaporator without recording pressure drop before and after.
• Forgetting to check water chemistry after the system is refilled.
• Using a ventless propane heater in a chiller room without ventilation or CO monitoring.
• Putting filters and panels back before the coil is fully dry.

The fundamentals of McQuay HVAC maintenance haven’t changed: keep the heat exchange surfaces clean, move the right amount of air and water, and prove the work with measurements. How we execute that has changed. Pressure washers and guesswork are out. Baselines and verification are in.

There’s something satisfying about seeing a clean evaporator coil pull the delta T back to normal. It’s simple, measurable, and worth doing right.