The compressed air dryer is creating a significant pressure drop -- either from clogging, icing, or being undersized for the airflow.

What you'll see

Pressure before the dryer is good, pressure after the dryer is noticeably lower. The drop gets worse over time or under high flow. In refrigerant dryers, the evaporator can ice up and partially or fully block airflow. When the dryer is bypassed, system pressure meets requirements -- confirming the dryer is the restriction.
Before you assume this is the problem

See all causes of pressure drop →

How to diagnose

  1. Measure pressure before and after the dryer

    Check the pressure drop across the dryer during loaded operation. A properly sized dryer in good condition should have minimal drop (0.1-0.3 bar). More than 0.5 bar indicates a problem.

    Result: High drop across dryer = restriction.

  2. Bypass test

    If your installation has a bypass valve, open it and close the dryer valves. If system pressure normalizes, the dryer is confirmed as the restriction.

    Result: Pressure normal on bypass = dryer is the problem.

How to fix it

  1. Service or replace the dryer

    Check for iced evaporator (hot gas bypass valve failure), clogged internal filters, or an undersized dryer. Service as needed. If the dryer is simply too small for the airflow, replace it with a larger one -- one size up is a good practice.

Common mistakes

Running on bypass permanently 'because the dryer causes pressure drop' means you now have water in the air. Fix or replace the dryer properly.

Parts & tools

Dryer service parts. Possibly a larger replacement dryer.

Review safety precautions before starting →