The HVAC Replacement Checklist: From McQuay Chiller Parts to Smart Thermostats

If you're trying to figure out whether to repair or replace your HVAC equipment—a commercial chiller, a hot water heater, or an outdated thermostat—this checklist is for you. It's built from real emergency calls, not a textbook.

I've spent the last 12 years coordinating urgent HVAC jobs. Some are same-day turnarounds for food processing plants; others are simple 80-degree afternoons where a church's AC died. In all that time, I've noticed the same pattern: the customers who call me in a panic had all the warning signs weeks earlier. They just didn't have a plan.

This checklist has six steps. Follow them in order, and you'll know exactly whether to repair or replace—and what to ask when you call for help.

Step 1: Identify What You're Really Working With

This sounds obvious, but you'd be surprised. A facility manager once told me he needed a "new compressor" for his McQuay chiller. He didn't know if it was a screw compressor, reciprocating, or centrifugal. We had to send a tech out just to read the nameplate—that cost him $150 and a day of lost time.

Here's what you need to document:

• Manufacturer and model number (e.g., McQuay WSC series)
• Compressor type (screw, centrifugal, scroll, reciprocating)
• Refrigerant type (R-134a, R-410A, etc.)
• Serial number and year of manufacture
• Capacity in tons or BTUs

For residential systems, the same principle applies. Do you have a furnace, a boiler with radiator covers, a heat pump, or a central AC? Each one has a different failure profile. And remember: a hot water heater is not the same as a boiler. Boilers heat your home; hot water heaters heat your tap water. Mixing those up on a phone call will waste everyone's time.

Step 2: Check the Age—and the Service History

HVAC equipment doesn't last forever. According to the ASHRAE Handbook—HVAC Systems and Equipment, the median service life for a screw compressor chiller is around 20 years. Hot water heaters typically last 8–12 years, depending on water quality and maintenance. If your unit is in that range, you're living on borrowed time.

But age alone isn't the whole story. I've seen a 25-year-old McQuay screw compressor that was running fine because it had been maintained by a disciplined team. I've also seen a 10-year-old unit that was a disaster because someone "saved money" by not doing annual preventive maintenance.

Pull out your service records. If the maintenance history is spotty, assume the equipment has hidden damage. If it's been religiously maintained, you can stretch the replacement decision, but you still need a plan.

Step 3: Separate Emergency Failures from Gradual Decline

This is where I earn my fees. A sudden failure is a different beast than a slow decline.

In March 2024, at 3:42 PM, I got a call from a cold storage operator. Their McQuay chiller had a seized screw compressor. The normal lead time for that exact replacement was 28 days. This operator had a warehouse full of perishable goods. We found a rebuilt compressor in Dallas, paid $2,400 in expedited freight on top of the $18,500 part, and had a crew working through the night. We got the chiller back up in 31 hours. The client lost maybe $12,000 in product—manageable. But if that compressor had failed a day later, or if we hadn't found the part, the loss would have been six figures.

The moral? Don't let a declining system become an emergency. If you've been nursing a chiller with frequent weird trips, low oil pressure, and increasing noise, the failure will come on your schedule, not the equipment's.

Step 4: Do the Math—Repair vs. Replacement

There's a rule of thumb I use: if a repair cost is more than 50% of the replacement cost of the whole unit, replace it. But that's only a starting point. You also need to consider:

• Availability of parts. McQuay chiller parts for newer units are usually easy to get, but for units older than 15 years, you might be waiting weeks. That downtime is a cost.
• Root cause. If you're replacing a compressor because of a refrigerant leak, the leak will kill the new compressor too. Fix the leak first.
• Efficiency. Newer chillers are significantly more energy-efficient. The energy savings can pay for the replacement over time.

I only believed the 50% rule after ignoring it once. We spent $800 repairing a hot water heater control board on a 10-year-old tank. Six months later, the tank leaked all over a finished basement. The replacement ended up costing $3,100 including water damage remediation. The $800 "repair" was a complete waste.

"The most expensive repairs are the ones you do twice."

Step 5: Understand What a Smart Thermostat Can—and Cannot—Do

People ask me all the time: "Can a Nest thermostat replace heating and air conditioning?" The answer is no. A Nest thermostat is not an HVAC system. It's a control device that tells your heating and cooling equipment when to run. If your furnace is dead, if your AC compressor is seized, if your hot water heater is leaking—a new thermostat won't help.

What a Nest can do is help you maximize an existing, functioning system. It can learn your schedule, adjust temperature automatically, and give you energy usage reports. But it needs compatible equipment. Most 24V systems—including gas furnaces, conventional ACs, and heat pumps—will work. Some high-voltage systems, electric baseboard heaters, and proprietary systems won't.

Here's the surprise: most people don't realize that a Nest won't work with a boiler system unless you have a compatible zone controller. It's not a universal upgrade. So before you buy one, check the compatibility tool and look at your current thermostat's wiring. If you have only two wires, you may need a C-wire adapter. If you're not comfortable with electrical work, call someone.

Step 6: Don't Forget the Peripheral Components

A replacement project doesn't end with the main unit. There are parts that affect comfort, safety, and code compliance that people routinely overlook.

For radiator heat: If your building has radiators, radiator covers are more than a decorative upgrade. They prevent burns—especially important in homes with children or elderly occupants—and can actually improve heat distribution. If you're already having a heating professional in, ask them to remove a radiator cover so you can see the valve and line condition.

For hot water heater replacement: You can't just swap the tank. Local plumbing codes require a proper pressure relief valve, a discharge tube, and in many areas, an expansion tank. Miss these, and your new water heater could fail inspection—or worse, create a safety hazard. The cost of code compliance is a small fraction of the replacement job.

I have mixed feelings about smart thermostats for old buildings. On one hand, they save energy. On the other, they create a false sense of security—people think their system is "smart" and ignore the mechanical issues. A thermostat is only as good as the equipment it controls.

Common Mistakes to Avoid

Let's finish with the mistakes I see, over and over, in emergency situations:

1. Ordering parts without the serial number. I've had customers order a McQuay screw compressor based on "chiller model" alone. The compressor model is stamped on the compressor itself, not always the chiller. Get the exact part number.
2. Repairing a symptom instead of the problem. If a compressor fails, don't just replace it. Why did it fail? Superheat set incorrectly? Overflowing condenser? Do the diagnostic work.
3. Thinking a smart thermostat can solve a mechanical failure. It won't. It's a thermostat, not an HVAC technician.
4. Ignoring permit and code requirements. Hot water heater and HVAC replacements require permits in most jurisdictions. Inspections catch problems that could become safety issues.

Here's the bottom line. Work through these six steps before you're in an emergency. If you already are in one, at least you'll know the right questions to ask—and you'll be less likely to make a panic decision that costs you twice as much in the long run.