The aftercooler is dirty, damaged, or its fan has failed. Hot, moisture-laden air goes straight to the system, overwhelming the dryer and drain.

What you'll see

Excessive water in the system even with a dryer. The air coming out of the compressor is much hotter than normal. Without a functioning aftercooler, the dryer receives air at 80-90 degrees C instead of the expected 40-50 degrees C. The dryer can't handle this much moisture and heat, and condensate overwhelms the system.
Before you assume this is the problem

If the aftercooler outlet air temperature is normal (within 10-15 degrees C of ambient), the aftercooler is fine. Look at the dryer and drains instead.

How to diagnose

  1. Measure aftercooler outlet temperature

    The air leaving the aftercooler should be within 10-15 degrees C (18-27 degrees F) of ambient temperature. If it's much hotter, the aftercooler isn't doing its job.

    Result: Outlet much hotter than ambient + 15 degrees C = aftercooler problem.

  2. Check the aftercooler fan and cooling surfaces

    Is the fan running? Are the cooling fins clogged with dust? The aftercooler sits right next to the oil cooler and gets equally dirty. Same cleaning applies -- blow with compressed air in reverse direction, or wash with soap and high-pressure water if oily.

    Result: Fan not running or fins clogged = clean or repair.

How to fix it

  1. Clean the aftercooler

    Clean the external fins, verify the fan works, check for internal blockage. The aftercooler is one of the most neglected components -- it sits next to the oil cooler and should be cleaned at the same time during every service.

Common mistakes

People focus on the dryer when the real problem is the aftercooler. The aftercooler does the heavy lifting -- it removes the majority of moisture (from our example: 16 liters/day down to 3 liters/day). The dryer handles the remaining 3 liters. If the aftercooler fails, the dryer gets overwhelmed.

Parts & tools

Aftercooler fan motor if failed. Cleaning supplies for the heat exchanger. Temperature gun for measuring inlet/outlet temperatures.

Review safety precautions before starting →