Whenever a Kaeser compressor shuts down with a fault code — or worse, runs but doesn't perform — the temptation is to start guessing. Put in a new filter. Call a technician. Maybe kick the control panel (don't do that).
After four years of managing compressed air quality at a mid-sized manufacturing plant — inspecting every service deliverable before it gets approved — I've learned that the guess-first approach is the most expensive habit you can have. When I implemented our equipment verification protocol in 2022, the most valuable change wasn't new machinery. It was teaching people to diagnose before they repair. There is no universal answer in Kaeser air compressor troubleshooting. The right next move depends on which type of problem you're facing.
In my experience, problems fall into three scenarios:
- Fault codes — the Sigma Control is telling you something specific.
- Performance drops — no codes, but the output is wrong.
- Moisture damage — the compressor is fine, but your air quality is not.
Each requires a different approach. Let me walk you through them.
Scenario A: Your Kaeser Compressor Shows a Fault Code
The good news: a fault code is not a verdict. It's a starting point. The machine is telling you what to inspect.
Here's a condensed list of Kaeser compressor fault codes I've logged on our own machines and during vendor audits. These are the ones that show up again and again:
- 100 / 101 — Motor overload. Check current draw on all three phases. Common in summer when ambient temperatures rise.
- 103 — Starter fault. Usually a wiring or contactor issue between the starter and the Sigma Control. Check the harness before suspecting the motor itself.
- 110 — Pressure sensor fault. The sensor is reading outside its expected range. Swap it with a known-good sensor to confirm.
- 120 — Emergency stop circuit engaged. Look at the E-stop button itself, then the circuit wiring.
- 130 — Fan motor overload. The cooling fan is struggling. Clean the fan, check the bearings.
- 150 — High discharge temperature. This one matters. Check ambient temperature, oil level, and cooler condition. If it recurs, you may have a deeper cooling issue.
- 160 — Low oil pressure. Check the oil filter first, then the pressure relief valve.
Why does the exact code matter? Because it turns a machine-wide search into a system-level investigation. The code may not name the root cause — a 150 can be triggered by a clogged cooler just as easily as a failed oil thermostat — but it tells you where to begin.
Now, the part I have to warn you about: don't just reset the code and walk away. In my first year at this job, I made exactly that rookie mistake. Cleared a 150 code, watched everything return to normal, and left it alone. Three days later, the compressor tripped again in the middle of the night shift. That failure cost us a $600 emergency service call plus a full night of lost production. The root cause was a partially blocked oil cooler, and I'd written it off as a sensor glitch. Since then, our protocol has been simple: log, inspect, reset, monitor.
Oh, and one more thing: keep a service history that includes the codes. When our Kaeser technician arrives, the first question they ask is for the fault history. Handing them a timestamped list is the difference between them arriving with the right parts and making a second trip.
Scenario B: The Compressor Runs, but Performance Is Off
This is the tricky scenario because there's no code to guide you. The Sigma Control reads normal, the compressor cycles, but the plant doesn't feel right.
What we typically see:
- Pressure drops under load more than it used to
- Recovery time after peak demand has gotten noticeably longer
- Oil mist at the vent, or oil in the condensate
No code, yet something is wrong. I look at three things, always in this order:
First — the inlet filter and oil separator. This sounds too obvious, and replacing expensive filters is easy to postpone. But a clogged separator raises the pressure differential across the system and directly increases oil carryover. What I mean is: the separator isn't a "maybe later" item. It's a vital sign. We track differential pressure across the separator, and when it crosses the Kaeser-specified threshold, the replacement gets scheduled. Not optional.
Second — the actual demand profile. This one makes people uncomfortable because it's not a compressor failure. I should add that I've been on both sides of this conversation. If your facility added a new line, changed shifts, or expanded tooling, you may simply be asking more of the compressor than before. The machine isn't worse — it's undersized for the new demand.
Third — the load/unload settings. Sometimes someone adjusts the pressure band to save energy, and the compressor starts short-cycling. This is one of the easiest corrections if you know how to use air compressor controls properly. If you don't, this is the moment to open the manual or ask your service rep to walk you through it.
There's also the equipment-class question. A Kaeser industrial rotary screw compressor is engineered for continuous duty and high uptime. A portable contractor-grade unit — say, a Dewalt air compressor — is a different animal entirely, designed for intermittent use and lower duty cycles. If a Dewalt won't hold pressure on a job site, the diagnosis often starts and ends with duty cycle. Apply the same standard to a Kaeser: if a rotary screw can't hold pressure under normal plant demand, that's unusual, and it deserves a careful baseline check of supply voltage, ambient temperature, and known maintenance history before you suspect the machine itself.
Put another way: you cannot judge a machine's performance against a spec that doesn't fit its class. Duty cycle matters, and knowing it is part of the diagnostic process.
Scenario C: Moisture in Your Air Lines
If the compressor starts, runs, holds pressure, and still your end product is suffering from water — cloudy finishes, clogged nozzles, corroded tools — then the issue isn't the compressor. It's the drying stage.
Most Kaeser installations pair a rotary screw compressor with a refrigerated or desiccant air dryer sized for the system flow. But I've seen plants try to cut corners with a dryer from another application entirely, including automotive-style units like the Bendix air dryer. Don't get me wrong — Bendix makes solid products for commercial vehicle air-brake systems. But a Bendix air dryer is designed around a different pressure range and moisture requirement than a stationary plant air system. The connections may fit, but it's answering a different question.
If your processes demand clean, dry air, check against compressed air quality expectations like ISO 8573-1. That standard defines acceptable moisture and particulate levels for different applications, and it gives you a measurable target instead of a guess.
Here's the moisture troubleshooting checklist:
- Check the dryer's dew point setting. Someone may have raised it to save energy. Wet air is the price.
- Check the inlet temperature to the dryer. If the compressor discharge is hotter than the dryer's rated inlet, the dryer can't remove moisture fast enough. A warmer-than-expected summer will expose this immediately.
- Check the condensate drains. This is the $15 fix that solved a $15,000 headache for us. Blocked drains equal water carryover, guaranteed.
There's something satisfying about this particular diagnosis when it lands. After chasing a moisture defect through an entire production line, tracing it to a single stuck drain valve — that's the payoff. In our Q1 2024 quality audit, moisture exposure accounted for 18% of our defect rate on packaging materials. We corrected the dryer specification and set a weekly drain maintenance schedule. By Q2, the defect rate dropped to under 3%. The total cost of the fix was roughly equivalent to what a single rework batch would have cost us.
How to Tell Which Scenario You're In
By now, your situation probably fits one of the three. But here's a decision guide, because it's easy to start down one path and go deep before realizing you were in the wrong scenario. The question isn't first "what's wrong with the compressor?" It's "which type of problem is this?"
Ask yourself these three questions:
1. Is there a fault code displayed?
Yes → Scenario A. Write down the exact code and timestamp. Do a visual check of the obvious systems: filters, belts, fans, oil level. Then fix or call.
2. Is the machine running, but output is worse than expected?
Yes → Scenario B. Start with the filters and separator. Verify the demand profile hasn't changed. Check control settings. At least, that's been my experience — and it has saved us from replacing parts that weren't actually worn.
3. Is the end product or process showing water damage?
Yes → Scenario C. Look at the dryer before the compressor. And I should add that most moisture issues we've logged were downstream of the dryer, which makes the dryer the natural starting point.
This approach is really quality control discipline applied to equipment. You wouldn't accept a production batch without inspecting it against spec, so don't accept a compressor's behavior without checking it against its design basis. The equipment is the heart of your compressed air system — but it's not the whole system. Maintaining the conditions around it is where your best return on effort is.
When to call the professional. I'm a fan of in-house troubleshooting when it's done safely. But there's a line, and I've crossed it enough to recognize the limit:
- Code 150 or 160 keeps returning after your initial fix.
- The compressor produces unusual vibration or noise that wasn't there before.
- You've gone through the checks above and still cannot explain the behavior.
In these cases, your Kaeser service partner has diagnostic software that goes far beyond the Sigma Control screen. There's no shame in getting a second set of experienced hands — the cost is small compared to the cost of being wrong at scale.
The bottom line: quality problems are rarely random. They follow patterns, and patterns can be diagnosed. With the right scenario in mind, you're not guessing anymore.
