Compressor Will Not Load to Compress Air
When Your Compressor Runs But Doesn’t Actually Compress
Your compressor is on. The motor is spinning. But there’s no air building in the tank or system, and no load sound either. If it feels like your machine is idling in neutral, you’re likely dealing with a load failure. Here's how to troubleshoot it based on your compressor type: reciprocating, portable rotary screw, or stationary rotary screw.
If You Have a Reciprocating or Portable Rotary Screw Compressor
These units should load automatically once pressure drops below the cut-in point. If the motor is running but you’re not hearing compression build (or the gauge isn’t moving) you might have a mechanical or control issue.
Check for These Problems:
- Pressure Switch Misadjusted or Faulty – The unit may think pressure is too high and stay in an unloaded state.
- Unloader Valve Stuck Open – This keeps the pump from building pressure even though the motor is running.
- Inlet Valve Jammed or Failing (Portables) – If the valve stays closed, no air gets compressed.
- Motor Spinning, But Pump Not Engaging – Could be belt slippage or a mechanical disconnect.
Steps to Fix It:
- Check and reset the pressure switch to match your unit’s PSI range.
- Inspect the unloader valve and replace if it’s stuck or damaged.
- On rotary portables, verify the inlet valve is opening fully under load.
- Check belts for tension and condition. Tighten or replace as needed.
If You Have a Stationary Rotary Screw Compressor
Rotary screw compressors use solenoids and sensors to determine when to load. If the unit is powered on but won’t load - or is just blowing air out the vent - something’s preventing the air end from engaging.
Common Issues:
- Load Solenoid Failure – If the solenoid doesn’t energize, the inlet valve won’t open.
- Inlet Valve Stuck Closed – This physically blocks airflow into the compressor element.
- Controller Settings or Fault – A system protection or fault condition may be blocking the load signal.
- Wiring or Sensor Malfunction – If the controller isn’t receiving proper input, it may hold the unit unloaded.
Diagnostic Steps:
- Cycle power to the machine and monitor if the solenoid energizes.
- Manually test the load solenoid and check for airflow when energized.
- Inspect the inlet valve for movement. Clean or replace if sticking.
- Review controller logs for fault conditions blocking load operation.
How to Prevent Load Failures
For Reciprocating and Portable Compressors
- Keep your unloader valve clean and replace it every 1–2 years depending on use.
- Check belt tension monthly and replace belts annually for heavy-use machines.
- Test your pressure switch during oil/filter changes to verify proper cut-in/cut-out behavior.
For Stationary Rotary Screw Compressors
- Inspect and test your solenoid valves during each scheduled maintenance interval.
- Clean and lubricate your inlet valve according to manufacturer specs.
- Review and back up your controller settings quarterly to ensure consistent performance after service calls or power failures.