If you've ever hit the Atlas Copco air compressor reset button and watched the fault light go away, you know that tiny moment of relief. I felt that relief four times in one week in November 2022. That week cost me about $1,800 and taught me a lesson I now use to train every new mechanic in our shop.
I'm not a trainer by title. I'm the guy who handles Atlas Copco rental fleet service orders for a regional equipment company. I've been doing it for eight years now. I've made and documented 11 significant mistakes in that time, totaling roughly $26,000 in wasted budget. The XAS 185 story is the one I put at the top of the checklist.
The first reset
It started with a customer renting our Atlas Copco air compressor XAS 185. That's a portable diesel unit, about 185 cfm, used on small contracting jobs. The customer called Monday morning: 'High temperature fault. Machine won't restart.' My first thought was dirty cooler. These units work on construction sites where they chew through dust and packing materials. So I told a tech to clean the radiator, check the air filter, blow out the oil cooler, press the reset, and run it for 15 minutes.
The tech called back. The Atlas Copco air compressor reset cleared the fault. It ran fine at low load. We thought it was solved.
Three more resets
Tuesday, same call. Wednesday, same call. Each time, someone went out, cleaned the cooler a little more, hit the reset button, and the machine started. Each time it failed later under load.
After the third call, the customer sent a video of the machine running. The display showed the high-temperature alarm. When he pressed the Atlas Copco air compressor reset, the screen cleared, the engine cranked, and the machine ran. It looked healthy for about ten minutes. Then the same alarm came back. In the background of that video, the cooling fan was visible. It wasn't spinning.
I knew we should load-test it. I knew the cooling fan wasn't spinning. But I thought, 'What are the odds it's the same fan motor we replaced six months ago?' The odds caught up with me.
To be fair, the customer was a small contractor. We had bigger accounts that week. It would have been easy to keep treating this as a nuisance reset and let the small guy wait. But the small guy had a crew standing around. Small doesn't mean unimportant. It means a crew standing around waiting, which is exactly the kind of customer you shouldn't fail.
The day I actually looked
On Friday, I drove to the lot myself. We had the unit inside with the side panel open. The bay heater was down, so we had a buddy heater on the floor to keep our fingers warm while testing the wiring.
That's when it hit me. I was standing in front of the machine, feeling warm air from the radiator on my face. Wait, I shouldn't be feeling that. There was no air being pushed. The cooling fan wasn't spinning. At all.
The XAS 185 uses a hydraulic fan drive to pull air through the oil cooler and radiator. When that fan drive loses pressure, the fan stops, the compressor builds heat under load, the controller sees the high temperature, and the machine shuts down. The reset clears the active fault code. It does not fix the fan. It doesn't even tell you to check the fan.
I told the tech to shut it down before it got worse. The temperature gauge was already climbing toward the red zone, and the engine wasn't even under full demand. With the fan dead, the machine would have tripped again even if we had never pressed reset.
What a buddy heater and a heat pump have to do with it
Here's the part that finally made me understand the failure. A buddy heater makes heat by burning propane. It creates heat. A heat pump, on the other hand, doesn't create heat—it moves heat from one place to another. You could ask what is a heat pump and get a long HVAC answer, but the short version is: a heat pump is a machine that moves heat around.
An air compressor's cooling system does the same job. It doesn't create cold. The fan moves hot air away from the radiator and oil cooler. If the fan stops, the heat doesn't move, and the temperature climbs. The reset button is just the symptom remover. The fan is the heat mover. Without it, you're asking a safety switch to be a spare part.
The real cost of the reset
We replaced the hydraulic fan drive motor. That part was about $450. Hydraulic oil, filters, and cleanup came to about $300. Truck rolls and labor were another $550. The unit was off rent for two days, so the rental replacement and lost income added roughly $500. I want to say the total was $1,780, but don't quote me on the exact number. The point is, it was north of $1,700, and every dollar came from me treating a reset as a fix.
Lots of people told me to always check the fan under load. I didn't listen. I only believed it after paying that exact cost. That customer went with another rental company for their next job. I'm not saying it was only because of this failure, but I also can't argue with the timing.
The checklist that would have saved me
That was the third time in four years I made a version of the same mistake. It took me four years and about 150 service calls to understand that a fault code is the beginning of a diagnosis, not the end of one.
Now, any time we get an Atlas Copco air compressor reset request in our fleet, we follow the same short list:
- Check airflow through the coolers with the engine running.
- Confirm the fan is turning or the fan circuit has pressure.
- Run the unit under load for at least 30 minutes before clearing the fault.
- Document what the temperature gauge does during the test.
That last step feels boring, but it's the step that catches what the first few resets miss. Trust me on this one. The reset button is not a repair.
That approach works for our rental fleet. At least, that's been my experience with portable diesel compressors.