Aircon Cassette Weak Airflow, Corroded Motor

Case Details

What We Checked

• Filter was actually clean — not the cause.
• Motor voltage under load was 15% below specification.
• Visible corrosion at the motor terminal connection points on the PCB.

The Diagnosis

The west-facing location of the unit meant salt air exposure over the years. Corrosion at the motor contact points had built up, creating resistance in the voltage path to the motor. The motor was receiving less power than it needed to run at full speed, so the fan slowed down even though the unit was trying to run it at full.

What Fixed It

The motor itself is fine. The problem is the corroded connection. Cleaning the contact points, applying a protective coating, and confirming the voltage returns to spec will restore the airflow. No motor replacement is needed.

After the corroded contacts were cleaned and protected, motor voltage returned to normal. Airflow strength came back to what it was before the corrosion started. The unit has been running at full capacity since the repair.

Why This Happens

Weak airflow is not always a blocked path.

• A cassette with a clean filter that still pushes weak air often has a voltage drop at the motor, not a blockage downstream.
• Corroded contact points at the motor reduce the voltage it receives, slowing the fan even when the filter is clear.
• Testing motor voltage under load is the fastest way to rule out a blockage and find the real cause.