If it’s time to change recirc air filters in your cab, go a little further and check the evaporator for caked-on dirt that can hamper its performance.
During normal operation, the evaporator picks up moisture from the air which condenses on the fins as water droplets before draining out of the system. This dehumidification action helps make the operator feel more comfortable in the cab.
The downside is that moisture on the fins attracts dust. We see this a lot on backhoes, skid steers, and other equipment where the operator runs the A/C with the window open so he can communicate with a coworker on the ground.
Most filters for recirculated air are the low-restriction type. They aren’t designed to remove large amounts of dust from the air before it reaches the evaporator. Next time you change the filter (following recommended inspection intervals), check the evaporator. It may need a good cleaning to make sure the operator is getting the steady stream of cool air he expects.