The compressed air dryer is running but not drying properly. Air leaves the dryer still saturated with moisture.

What you'll see

Water in the lines despite having a dryer installed. The dewpoint indicator on the dryer shows a higher temperature than rated (should be 1-5 degrees C for a refrigerant dryer). Or there's no dewpoint indicator and you just see water appearing where it shouldn't.
Before you assume this is the problem

Check that the aftercooler drain is working -- the aftercooler removes the bulk of the moisture. If the aftercooler drain is blocked, the dryer receives far more water than it's designed to handle.

How to diagnose

  1. Check the dewpoint reading

    A refrigerant dryer should produce a pressure dewpoint of 1-5 degrees C (34-41 degrees F). If it's reading higher, the dryer isn't working properly. If there's no dewpoint indicator, install one -- flying blind on dewpoint causes problems.

    Result: Dewpoint above 5 degrees C = dryer underperforming.

  2. Check the dryer condensate discharge

    Disconnect the dryer's water drain hose. Is condensate being discharged? A working dryer should produce noticeable condensate output.

    Result: No condensate = dryer not cooling air properly.

  3. Check for dryer overload

    If the dryer is undersized compared to the compressor, or if the incoming air is hotter than rated, the dryer can't achieve its rated dewpoint. Check the dryer's rated capacity against your actual airflow and inlet temperature.

    Result: Dryer capacity less than compressor output = undersized.

How to fix it

  1. Service the dryer

    Clean the dryer condenser, check refrigerant levels, verify the compressor (refrigerant compressor inside the dryer) is running. Replace clogged filters inside the dryer.

  2. Install an appropriately sized dryer

    If the dryer is undersized, replace it with the correct capacity. When in doubt, go one size up -- an oversized dryer has lower pressure drop and better dewpoint performance.

Common mistakes

For applications requiring very low dewpoint (below 0 degrees C), a refrigerant dryer cannot achieve this. You need a desiccant (adsorption) dryer. Don't expect a refrigerant dryer to do what it physically cannot.

Parts & tools

Dewpoint indicator if not already installed. Dryer service parts. Possibly a larger or different type of dryer.

Review safety precautions before starting →