You are now at the portable air compressor section of the largest online troubleshooting and repair guide for air compressors. This section deals with problems with portable air compressors. These are also called diesel-driven air compressors or tow-behind air compressors.Portable air compressors are the work horse of building and construction sites, but are often ‘abused’ and have quite a hard life.Here is a list of the most frequently asked questions and problems.

Common portable air compressor problems

Compressor will not start (completely dead)

Check battery. These compressors usually have a battery isolation switch, check if it’s on. Check if the compressor has tripped on a safety switch.

Compressor will not start (doesn’t crank)

Check if the compressor hasn’t tripped on a safety switch. Check all electrical connections. Check if safety switch isn’t pressed.

Compressor will not start (cranks, but diesel engine won’t start)

A diesel engine needs only two things to start: compression and fuel. Check the fuel system first, as this is the most common problem.

  • Check if there is fuel in the tank
  • Replace fuel filter
  • Pump priming pump (on top of fuel filter, if installed)
  • Vent low-pressure fuel system to remove any air
  • Vent high pressure fuel system to remove any air
  • Check stop solenoid and speed setting.

Portable diesel driven air compressors have a stop solenoid. It cuts off the fuel supply to stop the engine. Sometimes, this valves gets dirty or breaks down.

Check speed setting at start up. Speed lever is normally at ‘full rpm’ when compressor is stopped.

Compressor will not load / no pressure

Problem with loading/inlet valve. Check if loading/inlet valve opens. Check control system. Loading valve is 99% of the time opened/closed by control air. The control air comes from the regulating valve.

Engine does not rev up

Check speed setting lever. It is usually controlled by the speed actuator (pneumatic cylinder). The actuator is controlled by the same control air as the inlet/loading valve, and comes from the regulating valve.

Engine stops when loading

The engine doesn’t have enough power to turn the air compressor element. Causes could be:

  • Dirty air inlet filter (of engine)
  • Dirty oil filter
  • Speed controller failure
  • Valve clearance or timing wrong.
  • Dirty exhaust system (can happen when the compressor runs unloaded for a long time every day)

Oil in compressed air

Oil in compressed air can be caused by any of the following:

  • Dirty oil separator
  • Scavenge line plugged
  • Too high running temperature
  • Too high oil level
  • Wrong type of oil used

Be sure to properly stop the compressor. Shut all outlet valves and let it run idle before shutting it down.

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