How to Fix an Air Compressor

Replacing the unloader valve

If your air compressor starts up fine on the first start of the day, but stalls and makes a loud humming sound on subsequent tries, you’ve got a bum “unloader” valve. Air compressor repair can be simple. The air compressor unloader valve is what makes the “psssssst” sound when the motor shuts off after reaching operating pressure. It’s actually venting the residual pressure from the compressor head so the motor doesn’t have to work as hard on the next startup.

The air compressor unloader valve is usually built into the pressure switch assembly. Contact the air compressor  repair manufacturer to buy a new assembly. Or, remove the cover from the switch (unplug the compressor first) and locate the pressure switch part number.

Required Tools for this Compressor Repair Project

Have the necessary tools for this DIY project lined up before you start—you’ll save time and frustration.

Required Materials for this Compressor Repair Project

Avoid last-minute shopping trips by having all your materials ready ahead of time. Here’s a list.

Regular Replacement Parts

Regular checks of these elements and the regular replacement of filters should be part of your maintenance schedule before they become clogged, resulting in a loss of performance.

As another preventative measure to keep foreign particulate matter from entering the air compressor system, the inlet air filter should be replaced at regularly scheduled intervals or if an inspection indicates the need to replace the element.

Maintain the necessary quality of your lubricant with appropriately scheduled fluid changes and oil filter replacements that are geared to the activity of your system and working environment. Our fluid sampling program for rotary screw compressors will provide you with the necessary information to define the appropriate schedule for your air compressor.

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