Dor-Mar service technician cleans inside and outdoor AC condenser unit

Why is My Air Conditioner Making a Rattling Noise?

For most people, a rattling noise from a home air conditioner sets off alarm bells, as it should. There could be a number of reasons your AC is rattling, but it’s not necessary to panic.

There are a few all-too-common explanations for why your AC equipment is making a rattling noise.

  • Outdoor unit has collected debris
  • Loose panels or parts on the unit
  • A faulty or damaged motor
  • A bent or damaged fan blade

Fortunately, there are some things you can check as a homeowner before calling in the pros. Read on for details.

Issue: Organic or Other Debris in the AC Unit

Being located outdoors, with plenty of openings on the cover, the air conditioning unit allows debris like leaves, twigs, rocks and dirt to fall inside. Any number of these types of foreign objects can cause a rattling noise.

The rattling itself is not a big issue, but it’s what debris inside your AC system can do: cause damage, sometimes severe, requiring expensive repair or replacement of the entire unit.

A common problem in Ohio is those little white cottonwood seeds that seem to be attracted to the fins on your outdoor AC unit’s condenser. While they may not directly cause a rattle, they can cause plenty of trouble for the efficiency of your Air Conditioning system.

Solution: If there is plant growth on your AC unit, carefully trim it back and remove the clippings to ensure nothing falls into the grille. Optimally, we recommend you don’t allow growth any closer than three feet to the unit.

You can use a garden hose to spray the grille on the outside of your AC unit, but you’ll need a professional AC contractor to open the cover and thoroughly clean the inside, as well as a special solvent to help remove cottonwood seeds and grass clippings from the condenser fins.

Most importantly, a skilled AC service technician can check to be sure none of the parts in the unit were damaged from the foreign object, and if necessary, repair or replace the parts.

Issue: Bent or Damaged AC Fan Blades

The fan on the outdoor AC unit serves the important function of moving air across the condenser coil. Fan blades are made of thin aluminum or steel. A misaligned or loose fan blade can hit parts of the frame or casing, causing a rattling or scraping noise.

What could cause a fan to be damaged?

  • Age, or everyday wear and tear
  • Foreign objects, such as organic debris or rocks, to fall into the unit and bend or damage a fan blad
  • Improper alignment or installation

Solution: Replacing a damaged fan blade isn’t the most difficult task on an outdoor AC unit, but it’s best left to a professional AC repair service technician. The tech can also check to be sure the fan motor shaft isn’t damaged or bent as well, which could be catastrophic to the rest of the unit.

Issue: Faulty or Damaged Air Conditioning Motor

The typical outdoor AC unit contains a fan mounted to a motor, usually at the top of the unit. Motors contain bearings that wear out, dry out from lack of maintenance, or can be damaged or bent by foreign objects entering the unit. The fan motor can make a screeching or whining noise when the bearings begin to wear out, but if the motor shaft is bent or out of balance, it can create a pretty nasty rattling noise from the loose moving parts (that aren’t supposed to be loose).

Solution: Not really a do-it-yourself project, replacing an AC fan motor can be done affordably and quickly by a professional AC service technician. A damaged motor must be replaced quickly before it causes damage to other parts of the unit.

Issue: Loose Cover or Panels on Outdoor AC Unit

If your outdoor AC unit has been serviced recently (or opened by a curious homeowner), chances are the cover panel wasn’t reinstalled correctly or completely. The cover is held down by a number of self-tapping sheet metal or machine screws, and if not installed correctly or tightened adequate, the vibration caused by the fan motor can cause those screws to loosen even more.

Solution: Finally, if you’re relatively handy, this is absolutely something you can take care of yourself. Typically, you’ll need either a Phillips tip screwdriver or a ¼” nutdriver or socket to tighten the fasteners.

If the AC unit is still making a rattling noise after tightening the cover panel(s), it is definitely time to contact a professional AC technician to check the unit out.

For best results, why not just go ahead and have a spring AC tune-up performed on the entire system? Spring is the perfect time to have the system serviced, well before the high temperatures of summer require you to run the unit full blast and all day.

More Reasons Why Your Air Conditioner May Make a Rattling Noise

If you’ve checked out out the short list above and ruled out any of the causes, there are other potential reasons why your AC system is rattling:

  • Ductwork Too Small. Back pressure from undersized ductwork can cause your blower motor to work too hard, causing a rattling noise.
  • Damaged or Missing ISO Pads. These are pads installed beneath the compressor unit to reduce noise and vibration transfer to the house.
  • Furnace (or the Air Handler) Not Installed Properly. If your furnace is installed in the attic, a furnace that isn’t level can cause vibration to be transferred to your roof trusses, making a rattling noise.
  • Dirty or Clogged Air Filter. This can also cause your blower motor to overwork, causing a rattling noise (especially if excess debris is caught in the filter).
  • Furnace Blower Motor or Squirrel Cage Out of Balance. Although this sound would originate from the furnace unit, it could be easily mistaken as coming from the ductwork. This is the motor than moves the air past the air handler, across the evaporative coil (aka the A-Coil) and out into the home.
  • Damaged or Worn Out Register. This might be an issue, especially in older homes. Most heat registers are made from inexpensive aluminum or thin steel and can become damages or worn out over time. Since air exits the ductwork out into the home, this can cause a vibration or rattling noise.

If your home’s air conditioning system does require maintenance or repair, it’s important to hire the best AC contractor at the right price: Dor-Mar Heating and Air Conditioning.

We pride ourselves on our preparedness with highly-trained, certified air conditioning technicians who pilot fully-stocked service vehicles. We offer same-day appointments, so our techs can get there to quickly diagnose the problem. Often, because of truck stock, we can fix your AC system on a single visit or the same day.

How Dor-Mar Can Help

Our team offers a wide array of routine maintenance and emergency services for your heating and cooling system, allowing your family to breathe fresh, safe, clean air and be comfortable year-round. We also offer a number of add-ons to your HVAC equipment that can improve your home’s IAQ, such as electrostatic air filters, whole-house humidifiers, duct cleaning, and more.

Schedule an appointment for HVAC system troubleshooting or maintenance with us today by using our online contact form, or call one of our seven neighborhood offices listed below. We pride ourselves on our customer-focused service, and our reviews show it.

NEWARK  740.345.6639 • COLUMBUS 614.238.6689 • DUBLIN 614.545.8939 • REYNOLDSBURG 614.365.1579 • WESTERVILLE 614.381.1540 • GROVE CITY 614.595.3098 • ZANESVILLE 740.454.2420

Dor-Mar…Your Climate Hero!

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