AAON HVAC Units: What You Actually Need to Know (From a Guy Who's Installed a Bunch)
I've been a commercial HVAC service tech for about 12 years now. My company manages 60+ buildings across the southwest, and we've put in—I don't know—probably 150+ AAON units in that time, across different series and vintages. Not saying I know everything, but I've seen enough weird failures to know what questions actually come up.
Here's what I keep getting asked about AAONs, and my honest answers.
1. Is an AAON a good unit? I keep hearing different things.
Short answer: yeah, generally. Long answer: it depends on what you're comparing it to, and what generation you're getting.
Compared to a Carrier or Trane—which are the other big names in light commercial rooftop units—AAONs have always been solid. Their scroll compressor tech is reliable, and I've found them to be easier to work on than some competitors. The cabinet construction is robust.
But here's something vendors won't tell you: the earlier models with the single-speed compressors could be a bit rough on starting current. The newer stuff with digital scroll technology is much better. If you're looking at a used unit from before 2018-ish, factor in potential inrush issues.
My experience is based on mid-size commercial units (7.5 to 25 tons). If you're dealing with residential splits or massive industrial chillers, your experience might differ.
2. What does the outside air temperature sensor actually do on an AAON?
This is the number one question I get from facility managers who see a random sensor on their unit and panic. It's simpler than you think.
The outside air temperature sensor (OAT) is for economizer control and discharge air temperature reset. Basically, the unit looks at it to decide if it should use free cooling from outside air instead of running the compressor. It's a critical sensor for efficiency.
Most buyers focus on the compressor or the coil and completely miss this sensor. If it fails—and they do fail, they're cheap sensors exposed to weather—the unit might run the compressor when it doesn't need to, or it might lock out the economizer entirely. That kills your efficiency.
The question everyone asks is 'what's the part number?' The question they should ask is 'is the OAT actually reading correctly before I replace anything else?' I've seen a $45 sensor diagnosed as a failed controller twice.
3. How often do I really need to change the air filter in a commercial AAON?
It says every 30 days on the manual. Realistically?
Depends on the building. If your building is next to a construction site or a farm, every 30 days is not enough. I've pulled filters out after 2 weeks that looked like they'd been installed in 1995.
For a standard office building with decent pre-filtration (like MERV 8 or better), you can push it to 60-90 days if you're checking static pressure. But here's my rule: change it when the differential pressure across the filter hits about 0.5 inches of water column over clean. That's the data-driven way. Not 'every 30 days' just because.
Why does this matter? Because a clogged filter doesn't just reduce airflow—it forces the blower motor to work harder, which wastes electricity and reduces fan lifespan. And it can freeze the evaporator coil in cooling mode. Not great.
So glad I started using pressure gauges a few years ago. Almost went with a calendar-based approach indefinitely, which would have cost a fortune in premature motor replacements.
.4. Wait, can I use a space heater with my commercial AAON unit?
This is a slightly confusing question, I know. But I get it enough to answer it.
Yes, AAON units often have optional electric heat strips for backup or emergency heat. It's not a 'space heater' you plug into a wall—it's installed inside the unit itself. If you have electric heat strips, you can use them as a heat source. The unit's control board manages them.
But a standalone portable space heater? You can plug one in, obviously, but the building's electrical system and the HVAC zoning have to handle it. And if you're using a space heater because the AAON's heat is broken, fix the unit. The space heater is a band-aid that can cause issues if left unattended.
Honestly, I'm not sure why some people try to use a cheap 1500W space heater instead of fixing the $500 heat strip issue. My best guess is they're trying to avoid a service call fee.
In January 2024, a client called at 4 PM needing emergency heat for a 10,000 sq ft warehouse that was down to 45°F. Normal heat strip replacement is 2 days. We found a local supplier with the correct 18kW heat kit, paid $115 extra in overnight freight, and had it running by 10 AM the next day. Client's alternative was losing a $40,000 distribution contract due to temperature-sensitive goods.
5. Why would I buy a burner phone? This is about HVAC, right?
I know. This keyword makes no sense in context. But since we're here: no, you don't need a burner phone to buy or install an AAON HVAC unit.
Unless you're doing something illegal with the equipment, which I don't recommend (and voiding your warranty). Use your regular phone. Call the parts distributor. That's it.
A lesson learned the hard way: trying to save money on a 'burner phone' for service calls is stupid. Just use a work phone with a case. A cracked screen costs more than a burner phone anyway.
6. Where can I find authentic AAON replacement parts?
Good question. Counterfeit parts are a real problem in this industry.
Your first stop should be an authorized AAON distributor. There's a locator on their website. But if you're in a bind, a lot of quality HVAC parts distributors carry AAON-compatible parts, including compressors, coils, and controls. Just make sure they have a reputation.
What most people don't realize is that many 'AAON' parts online are actually generic replacements that may or may not work correctly. The coils especially—a cheap coil from a no-name supplier might leak after 2 years. I've pulled coils that looked fine but had micro-leaks at the brazed joints.
Our company lost a $12,000 contract in 2023 because we tried to save $800 on a replacement compressor from a discount vendor instead of buying factory-certified. The compressor failed within 4 months, and the client went with a competitor for the entire system replacement.
That's when we implemented our 'OEM-or-authorized-only' policy for critical components. It cost a bit more upfront but saved us in callbacks.
7. Do I need to worry about the pressure switch? It keeps tripping.
That's not a normal thing—it's a diagnostic thing. The pressure switch is a safety device. If it's tripping, something is wrong. Could be a dirty filter (see question 3), low refrigerant charge, a bad condenser fan motor, or even a clogged orifice inside the distributor.
Don't just reset it and hope it goes away. That's not troubleshooting, that's gambling. I've seen that approach lead to a $4,000 compressor replacement because the real issue—a failing TXV—was ignored for 6 months.
The fundamentals haven't changed: diagnose the root cause, not the symptom.
Bottom line on AAON units:
They're reliable, commercial-grade machines. Keep up with filter changes, pay attention to sensors, and don't skip on OEM parts for critical repairs. If you have a specific model and a weird symptom, I can probably point you in a direction, but I can't help with a burner phone purchase.
