Air Handling Unit Repair:
What Every Facility Manager Should Know

Introduction

Your air handling unit works around the clock, and when it starts to fail, the warning signs are usually there long before a full breakdown. Knowing what to look for can mean the difference between a simple repair and a costly emergency replacement.

At Denver Industrial Services, we specialize in diagnosing and repairing commercial and industrial AHUs across the Denver metro. Here's a breakdown of the four most common problem areas our technicians encounter, and what you should watch for.

‍

Pillow Block Bearings

Pillow block bearings support the fan shaft and allow it to rotate smoothly. Because they operate under constant load and vibration, they are one of the most wear-prone components in any AHU. Neglected bearings are a leading cause of unplanned downtime in commercial air handling systems.

Warning signs to watch for:

• Grinding, squealing, or rumbling noises during operation, early signs of lubrication failure or race damage
• Excessive vibration or wobble felt through the unit housing
• Overheating of the bearing housing, even brief overheating accelerates wear significantly
• Visible rust, corrosion, or grease leakage around the bearing mount
• Increased energy draw on the motor without any change in load

Regular lubrication and vibration analysis during scheduled maintenance intervals can extend bearing life substantially and prevent shaft damage.

Exhaust Fan

The exhaust fan is responsible for removing stale, contaminated, or excess air from the building. A failing exhaust fan doesn't just affect air quality, it throws off the entire pressure balance of your HVAC system, creating conditions that accelerate wear on other components.

Warning signs to watch for:

• Reduced or uneven airflow from exhaust registers or ductwork
• Musty odors, elevated humidity, or poor indoor air quality complaints
• Motor running hot, tripping thermal protection, or cycling on and off unexpectedly
• Visible blade damage, imbalance, or debris buildup on the impeller
• Unusual vibration or rattling during startup or shutdown

Belt-driven exhaust fans require regular belt tension checks; direct-drive units need motor and capacitor inspection. Both benefit from annual blade cleaning to maintain rated airflow efficiency.

Fan Housing

The fan housing (also called the scroll or volute) channels airflow efficiently from the impeller into the ductwork. Damage or deterioration here can sharply reduce system performance while going unnoticed on a casual inspection.

Warning signs to watch for:

• Visible corrosion, pitting, or holes, especially common in units handling humid or chemically laden air
• Air leaks detectable as hissing sounds or reduced static pressure at supply points
• Cracks, dents, or deformations that alter the internal clearance between wheel and housing
• Excessive noise caused by wheel-to-housing contact due to shaft misalignment or worn bearings
• Buildup of grease, dust, or biological growth inside the housing reducing effective throat area

Housing repairs often involve welding, patching, or full section replacement. Catching deterioration early makes the difference between a patch job and a full housing swap.

Unit Structure & Frame

The structural integrity of the AHU itself is often overlooked in favor of mechanical components, but a compromised frame can cause misalignment that accelerates wear on every rotating part inside the unit. Denver's temperature swings and freeze-thaw cycles put rooftop and outdoor units under particular stress.

Warning signs to watch for:

• Corrosion or rust on the base rail, frame sections, or panel fasteners
• Water pooling inside the unit or evidence of past flooding, accelerates internal corrosion rapidly
• Loose, missing, or deteriorated panel gaskets causing conditioned air bypass
• Sagging, warped, or cracked structural panels that allow frame flex under vibration
• Isolator pads or spring mounts that have failed, transferring vibration to the building structure

Structural repairs range from rust treatment and panel replacement to full base rail fabrication. A level, stable frame is the foundation everything else depends on.

Don't wait for a breakdown. Most AHU failures are predictable and preventable. A proactive inspection schedule — ideally twice per year for commercial units in Denver's climate — dramatically reduces emergency repair costs and extends equipment life.

Whether you're dealing with an active problem or want to get ahead of one, the Denver Industrial Services team provides on-site diagnostics, component repair and replacement, full unit rebuilds, and ongoing maintenance contracts across the Denver metro area.

‍