Overheating is one of the most common, and most ignored, problems in compressed air systems. Until the compressor shuts down mid-shift and your production line stops.
At AirSpace Machinery, we've seen this scenario play out hundreds of times. A factory calls us because their screw compressor keeps tripping on high temperature. Usually, the fix is simple. Sometimes it's not. Either way, the same checklist applies.
This is the exact troubleshooting checklist our engineering team uses when diagnosing overheating issues on PMV screw compressors. It works for most industrial rotary screw units. Print it out. Laminate it. Stick it on the compressor room wall.
Why Overheating Happens (The Short Version)
Screw compressors generate heat. That's normal. What's not normal is when the heat can't escape fast enough.
Overheating usually comes down to one of these four categories:
- Airflow problems , something is blocking cooling
- Oil problems , low level, wrong grade, or degraded oil
- Component failures , fans, thermal valves, coolers
- Environmental factors , room too hot, poor ventilation
Let's walk through each one.
Step 1: Don't Restart Immediately
If your compressor has shut down on a high-temperature fault, resist the urge to hit the reset button right away.
Let it cool down for at least 15–20 minutes. Restarting a hot compressor can cause:
- Oil foaming
- Bearing damage
- Repeated thermal trips
Use this time to start your inspection.
Step 2: Check the Air Filter
A clogged air filter is the #1 cause of overheating we see in the field. Restricted airflow forces the compressor to work harder, generating more heat.
What to look for:
- Visible dust or debris on the filter element
- Filter collapse or damage
- Differential pressure reading on the control panel (if equipped)
Fix: Clean or replace the filter. On dusty shop floors, consider upgrading to a higher-capacity intake filter or shortening your replacement interval.
Step 3: Inspect the Oil System
Oil in a screw compressor does more than lubricate, it absorbs and carries heat away from the compression chamber. If the oil system isn't working right, heat builds up fast.
Check these items:
| Item | What to Look For |
|---|---|
| Oil level | Should be visible in sight glass (mid-level when running) |
| Oil color | Should be clear amber, not dark or milky |
| Oil smell | Burnt smell = degraded oil |
| Oil grade | Must match manufacturer spec |
Fix: Top off if low. If the oil is dark, burnt-smelling, or has visible particles, schedule a full oil and filter change. Using the wrong viscosity grade is a common mistake, always check the manual.
Step 4: Clean the Cooler
The oil cooler and aftercooler are heat exchangers. If they're coated in dust, oil mist, or shop grime, they can't dissipate heat effectively.
What to do:
- Shut down and lock out the compressor
- Use compressed air (from another source) or a soft brush to clean the cooler fins
- Check for bent or damaged fins that reduce airflow
- On water-cooled units, check for scale buildup or low water flow
Pro tip: In high-dust environments, schedule cooler cleaning every 500 hours, not just at annual service.
Step 5: Verify the Cooling Fan
On air-cooled screw compressors, the fan is critical. If it's not moving enough air, nothing else matters.
Check:
- Fan is spinning freely (no obstructions)
- Fan is rotating in the correct direction (yes, this happens after motor replacements)
- Fan motor is not overheating or drawing excessive current
- Ducting to the fan is clear and unblocked
Fix: Replace worn fan belts, clean fan blades, and ensure any exhaust ducting leads outside the compressor room: not into a dead corner.
Step 6: Check the Thermal Valve
The thermal valve (also called thermostatic valve) controls oil flow to the cooler. When the compressor is cold, it bypasses the cooler. When it's hot, it routes oil through the cooler.
If the valve is stuck in bypass mode, the oil never gets cooled.
Symptoms:
- Compressor overheats quickly after startup
- Oil temperature rises even though cooler and fan are working
Fix: Test or replace the thermal valve. This is a common wear item on older units.
Step 7: Evaluate the Compressor Room
Sometimes the compressor itself is fine: but the room is the problem.
Environmental checklist:
- Ambient temperature below 40°C (104°F)
- At least 1 meter clearance around the unit
- Fresh air intake available (not recirculating hot exhaust)
- Exhaust ducted outside or to a well-ventilated area
- No heat sources nearby (furnaces, ovens, boilers)
Fix: Add ventilation fans, install exhaust ducting, or relocate the compressor. In extreme cases, consider switching to a water-cooled unit.
Step 8: Review System Pressure and Demand
Running a compressor at maximum pressure all day generates more heat. So does frequent loading and unloading.
Ask yourself:
- Is the system pressure set higher than necessary?
- Are there air leaks forcing the compressor to run longer?
- Is the compressor cycling on/off more than once every 15 minutes?
Fix: Lower discharge pressure if possible. Fix leaks. Consider adding a receiver tank to buffer demand swings. Our standard recommendation is a 1,500 L tank for systems in the 15–75 kW range.
Step 9: Check Electrical Supply
Low voltage or voltage fluctuations can cause motors to draw more current, generating excess heat.
What to check:
- Voltage at the panel matches nameplate rating (±5%)
- Wiring connections are tight and not corroded
- No tripped breakers or blown fuses
Fix: Have a qualified electrician inspect the supply. Voltage issues can also damage VSD drives on energy-efficient air compressor models.
Step 10: Use Your Control Panel
Modern screw compressors: especially PMV (Permanent Magnet Variable Frequency) units: have smart control panels that log temperature trends, fault codes, and operating hours.
Use this data:
- Check peak temperature over the last 24 hours
- Review fault history for recurring high-temp trips
- Monitor pressure drop across filters and separators
If your compressor has IoT connectivity, you can track this remotely. Our PMV screw compressors support cloud-based monitoring, so you can catch overheating trends before they cause a shutdown.
When to Call for Help
If you've gone through this checklist and the compressor still overheats, it's time to call a technician. Possible deeper issues include:
- Worn airend bearings
- Internal oil leaks
- Faulty temperature sensor
- Control board problems
On older units that overheat frequently, replacement may be more cost-effective than repeated repairs. A new energy-efficient air compressor with PMV technology runs cooler, uses less power, and pays for itself in 2–3 years.
Quick Reference: Overheating Troubleshooting Checklist
| Step | Check | Action |
|---|---|---|
| 1 | Compressor tripped | Let it cool 15–20 min |
| 2 | Air filter | Clean or replace |
| 3 | Oil level and condition | Top off or change oil |
| 4 | Cooler | Clean fins, check for damage |
| 5 | Cooling fan | Verify rotation, clear obstructions |
| 6 | Thermal valve | Test or replace |
| 7 | Room ventilation | Add airflow, check ambient temp |
| 8 | System pressure | Lower if possible, fix leaks |
| 9 | Electrical supply | Verify voltage, check connections |
| 10 | Control panel | Review logs and fault codes |
Need Help Diagnosing Your Compressor?
If your screw compressor keeps overheating and you're not sure why, our engineering team can help. We offer remote diagnostics, on-site support, and full system audits.
Get a Proposal : tell us your pressure (bar/psi) and flow (m³/min or CFM), and we'll recommend the right solution for your plant.
Reviewed by Engineering
Author: Penny Winston | AirSpace Machinery
Penny writes practical guides for plant engineers and maintenance teams, covering compressed air systems, energy efficiency, and equipment troubleshooting.
Sources & Standards
- Operating temperature limits based on ISO 1217 (Displacement Compressors – Acceptance Tests)
- Oil specification guidance per compressor manufacturer datasheets
- Ambient temperature recommendations per ISO 5388 (Stationary Air Compressors – Safety Rules)
- CE and ISO 9001 certification standards for AirSpace Machinery products
