A compressor always gets hot: compression turns a large share of the electricity it uses into heat. What is not normal is a temperature that climbs higher than usual, or a machine that cuts out in the middle of work. When that happens, the compressor is protecting itself: the cause is almost always around it, not inside it.
Safety first: let the machine cool down before doing anything. Switch off and lock out the power supply and release the air from the air receiver before opening a cover. The oil and the compressor unit can be very hot.
Diagnosis at a glance
| What you notice | Likely cause | What to do |
|---|---|---|
| The machine cuts out mostly in summer or in the afternoon | Room too hot, hot air recirculating | Improve the fresh air inlet and hot air outlet |
| The temperature has been creeping up for weeks | Cooler clogged with dust | Clean the cooler and grilles |
| Screw compressor: temperature fault even though the room is cool | Low oil level or worn oil | Check the level and the date of the last oil change |
| The machine runs hot and air flow drops | Clogged air filter | Clean or replace the air filter |
| Piston compressor: it runs almost non-stop | Demand too high or a leak | Compare demand with air flow, look for leaks |
| The motor cuts out, not the compressor | Motor electrical protection tripped | Have the power supply checked by an electrician |
1. The room: the number one cause
A compressor releases its heat into the room. If this hot air is not removed, the machine draws in hotter and hotter air to cool itself, and the temperature climbs until the safety shutdown. That is why stoppages often happen in summer, late in the day, or after a door has been closed or another machine added to the room.
- Check that there is a fresh air inlet low down and a hot air outlet high up, and that they are not blocked.
- Leave space around the machine, as stated in the manual: a compressor pushed against a wall recycles its own hot air.
- Compare the room temperature with the maximum ambient temperature given in the manual.
Our article on where to install your compressor covers how to set up the room.
2. A clogged cooler
On an air-cooled screw compressor, the oil passes through a cooler with air blown across it by the fan. A layer of dust, oil mist or sawdust stuck to the fins is enough to push the temperature up. It is a typical cause in joinery shops, body shops and dusty workshops.
With the machine stopped and cooled down, clean the cooler with a blow gun, from the inside out, and clear the intake grilles. On a piston compressor, clean the cylinder fins the same way, and the intercooler on a two-stage model.
3. Oil in a screw compressor
In a screw compressor, the oil absorbs the heat of compression. If there is too little, or if it has aged, it cools less well.
- Level: check it with the machine stopped, at the sight glass, and top up with the recommended oil.
- Condition: dark oil that smells burnt has already overheated. Milky oil contains water.
- Due date: a postponed oil change pushes the temperature up. On our screw compressors, the first service is at 500 hours, then every 1,500 hours.
For choosing the oil, see which oil for a screw or piston compressor.
4. The filters
- Clogged air filter: the compressor strains to draw in air, runs hotter and produces less air.
- Clogged oil filter (screw): the oil circulates less well and cools less.
- Saturated air/oil separator (screw): the machine strains to push the air through, uses more power and runs hotter.
Each screw compressor's service kit brings these three filters together. The full schedule is in when to service a screw compressor.
5. How it is used
- Undersized piston compressor: a piston compressor is not designed to run non-stop. If it hardly ever stops, demand exceeds what it can deliver, or a leak keeps it running for nothing. The configurator compares your demand with the machine's air flow, and our article on compressed air leaks helps you find them.
- Pressure set too high: the higher the pressure, the harder the compressor works and the hotter it gets. Set the pressure to what the tools actually need, without an excessive margin: see calculating your compressor pressure.
- The opposite, not enough heat: a compressor that only runs very short cycles never reaches operating temperature. Moisture then condenses in the oil, which turns milky. It is not overheating, but it is also a sizing problem.
Screw compressor: read the controller
On a screw compressor, the electronic controller constantly monitors pressure, temperature and operating hours, and stops the machine if something is wrong. Before restarting, note the message displayed and the temperature shown: they point straight to the diagnosis. Restarting several times in a row without looking for the cause only repeats the overheating.
When to call after-sales service
If the room is ventilated, the cooler clean, the oil and filters up to date, and the temperature still climbs, or if the machine cuts out with a fault message you do not understand, contact after-sales service. Have the model, serial number, operating hours, the message displayed and the room temperature at the time of the stop ready. To stop the problem coming back, our annual maintenance package has the machine checked at every service interval.
For your trade: Compressor for joinery workshops, Compressor for industry and production, Compressor for garages.