AC Making Noise
Unusual sounds from AC unit including banging, grinding, squealing, hissing, or clicking noises.
Quick Overview
DIY: 30-60 minutes | Professional diagnosis: 1 hour | Component replacement: 1-3 hours
Summer
Common Symptoms
You might be experiencing this problem if you notice any of these signs:
- Loud banging or clanking sounds
- High-pitched squealing or screeching
- Grinding or metal-on-metal sounds
- Hissing or bubbling noises
- Clicking that doesn't stop
- Buzzing from outdoor unit
- Rattling from vents or ductwork
- Humming that won't start
Step-by-Step Diagnosis
Follow these steps to identify the exact cause of your problem:
- Identify which unit makes the noise (indoor vs outdoor)
- Note exactly what the sound sounds like
- Determine when noise occurs (startup, running, shutdown)
- Check if noise happens constantly or intermittently
- Listen for location of sound within unit
- Note if noise changed from previous operation
- Check if outdoor fan blades are hitting anything
- Inspect for loose panels or covers rattling
- Verify noise isn't coming from ductwork
- Check if noise occurs only in certain modes
- Note if performance decreased with noise
- Record video of sound for technician if needed
Most Common Causes (Ranked by Likelihood)
Loose or damaged fan blade
HIGH LIKELIHOODDebris in outdoor condenser unit
HIGH LIKELIHOODFailed or failing capacitor
MEDIUM LIKELIHOODWorn compressor mounts
MEDIUM LIKELIHOODRefrigerant leak (hissing)
MEDIUM LIKELIHOODFailing blower motor bearings
MEDIUM LIKELIHOODCompressor failure
LOW LIKELIHOODLoose ductwork
HIGH LIKELIHOODDIY Solutions
What You'll Need:
- Screwdriver set
- Wrench set
- Flashlight
- Work gloves
- Duct tape or metal HVAC tape
Time Required: 30-60 minutes
Step-by-Step Instructions:
- Turn off power to AC at breaker
- Remove outdoor unit top cover or grille
- Inspect fan blade for cracks or looseness
- Tighten fan blade mounting nut if loose
- Remove all debris (sticks, leaves, grass) from inside
- Check for anything rubbing against fan
- Inspect all panels and covers for looseness
- Tighten any loose screws or bolts
- Clean condenser coils if dirty
- Verify compressor mounting bolts are tight
- Check indoor unit for loose blower wheel
- Secure any loose ductwork with metal tape
⚠️ Safety Warnings
- Always turn off power at breaker before opening unit
- Never stick hands or tools near spinning fan blades
- Capacitors hold dangerous electrical charge even when power is off
- Don't run unit if fan blade is cracked or damaged
- If you hear electrical buzzing with burning smell, call pro immediately
When to Call a Professional
Don't attempt DIY repairs if you experience any of these situations:
- Loud grinding or metal-on-metal sounds
- Screeching that continues for more than 30 seconds
- Hissing with visible oil spots (refrigerant leak)
- Compressor makes loud banging then shuts off
- Electrical buzzing with burning smell
- Clicking that prevents unit from starting
- Noise persists after cleaning and tightening
- Fan blade is cracked or damaged
- Sounds coming from sealed components
Prevention Tips
Stop this problem before it starts with these preventive measures:
- Keep 2 feet clearance around outdoor unit
- Trim grass and vegetation before they reach unit
- Schedule annual maintenance for lubrication
- Install sound-dampening pads under unit
- Replace worn parts before complete failure
- Keep outdoor unit level on its pad
- Don't store items against outdoor unit
Frequently Asked Questions
What does a bad AC compressor sound like?
A failing compressor makes loud banging, clanking, or grinding sounds at startup. It may click repeatedly trying to start but never engage. Some make a high-pitched screech. If your compressor is making unusual noises, shut down the system immediately - running it will cause more expensive damage.
Why does my AC make a loud noise when it turns on?
A single loud bang at startup is often normal as ductwork expands from temperature change. However, repeated banging, grinding, or screeching indicates problems like a failing capacitor, loose fan blade, or compressor issue that needs professional attention.
Is it safe to run AC if it's making noise?
Minor rattling or occasional banging is usually safe. However, continuous grinding, loud screeching, or any noise combined with burning smell should be shut down immediately. Running a damaged AC causes more expensive damage, especially to the compressor.
Related Problems
AC Not Turning On
Air conditioner completely unresponsive with no fan, no sounds, or display showing but nothing happens.
AC Short Cycling
AC turns on and off repeatedly in short bursts instead of running proper cooling cycles.
Poor Airflow
Weak air coming from vents, some rooms get little or no airflow, or reduced air pressure throughout home.