What to Do If Your HVAC Makes a Screeching Noise Post-Storm in St. Louis

Turn off your HVAC unit immediately, shut it off at the thermostat and the circuit breaker, then inspect for debris or damage. Check belts, fan blades, motor bearings, and electrical parts for wear or misalignment. Clean out leaves or branches lodged in the outdoor unit, tighten loose panels, and replace any frayed belts. If the screeching continues after these steps or you’re not comfortable doing them, call a trained technician.

 

Immediate Safety Actions

 

Before you do anything, protect yourself and your equipment:

• Shut off power at the thermostat or control panel so the system can’t start while you work.
• Locate your home’s circuit breaker box and switch off the breaker labeled “HVAC” or “Air Conditioner.”
• Wear work gloves and safety glasses to avoid cuts from sharp metal edges or debris.

 

Inspect Common Mechanical Causes

 

After the storm, branches, leaves or hail can jam moving parts:

• Fan Belt (for belt-driven blowers): This rubber belt connects the motor to the blower wheel. If it’s cracked, loose, or slipping, it will screech. Look for frays or shiny worn spots and replace the belt if needed.
• Blower Wheel: Inside your indoor air handler, a fan with curved blades spins to move air. If blade tips hit the metal cabinet, you’ll hear screeching. Remove the access panel, spin the wheel by hand, and check for wobble or bent blades. Straighten minor bends carefully or replace the wheel.
• Condenser Fan: In the outdoor unit, blades can bend from debris impact. With power still off, spin the blades by hand. If they scrape the housing, loosen the mounting screws slightly, realign the blade, then tighten screws firmly.
• Motor Bearings: Electric motors have bearings that let shafts spin smoothly. When bearings wear out or lose lubrication, they make high-pitched squeals. Some bearings in older motors have oil ports—add a few drops of machine oil. If sealed bearings hum or screech, the motor usually needs replacement.

 

Electrical Component Checks

 

Storms can harm capacitors and wiring, causing odd noises:

• Start/Run Capacitor: This small cylindrical part gives the motor an extra boost. A failing capacitor can cause a whining or screeching sound as the motor struggles. If you have a multimeter with a capacitance scale, you can test it yourself, but only if you know how to discharge it safely. Otherwise, let a pro handle it.
• Loose Wiring or Connections: Vibration from strong wind can loosen electrical lugs and screws. Inspect visible wires for frays, and gently tug terminals—if any wire moves, tighten its connector with a screwdriver.
• Contactor or Relay: These switches click on and off. If contacts burn or corrode, they can arc and make a sharp squeal. Look for dark spots on the metal contact surfaces. Cleaning them requires special tools, so consider calling a technician if you see heavy pitting.

 

Testing and Power-Up Procedure

 

After cleaning and tightening:

• Replace all access panels and secure screws or latches.
• Turn the breaker back on, then set the thermostat to “Cool” at least two degrees below room temperature to force a startup.
• Listen from a safe distance. If the screeching is gone, run the system through a full cycle to ensure it cools properly.
• If the sound returns, shut the system off again—don’t force it to run, as this can cause further damage.

 

When to Call a Professional

 

If you’ve checked belts, blades, bearings, and basic wiring but the noise remains, or you’re unsure how to test capacitors and motors safely, book a qualified HVAC technician. They have the training and specialized tools to diagnose complex electrical issues, realign components precisely, and replace worn parts without risk to you or your system.

If you need expert HVAC help after a storm, Hoffman Brothers serves residents in St. Louis and Nashville.