Learning Center » A/C & Heating » What to Do When Your HVAC Unit is Making Loud NoisesWhat to Do When Your HVAC Unit is Making Loud Noises Virtually everything in the world with moving parts eventually starts making a mysterious and troubling sound. Cars tend to be the worst culprits for this, but around the house HVAC equipment often runs a close second. And like cars, air conditioners have a number of moving parts, which means an air conditioner rattling sound can come from a number of different sources. Here we'll discuss some of the most common symptoms. But, please, don't go digging around inside your AC equipment unless you know what you're doing. Just to give you one example, condenser units have high-voltage capacitors that can give you a nasty shock even when the power is shut off; call an HVAC pro instead.Parts is PartsA standard central AC system is made up of three main "parts": the outdoor compressor/condenser unit, the indoor air handler (typically a furnace), and the network of air ducts (the same ones used by the furnace in winter).

An air conditioner rattling sound could come from within any of these three systems. Fortunately, the systems are far more distinct and easier to identify than anything under the hood of a modern car (which these days is slightly less approachable than the Batmobile). pressor SoundsThe outdoor unit of a central AC system is typically called a condenser, while the essential equipment inside is the compressor. The compressor has a big motor that, as you know, makes a lot of noise under normal conditions and also creates a lot of vibration. The vibration can lead to loose hardware, possibly in the compressor's mounts or elsewhere. This certainly could be your air conditioner rattling sound, especially if it sounds like rattling metal. There's a lot of vibration when the compressor starts up, and rattling that occurs during startup only is a pretty good clue that hardware is the culprit.Air Handler SoundsThe primary moving part on an air handler is the blower assembly, a big motor with a fan.

The motor or fan wheel can cause a rattling sound when your air conditioner is actively blowing air through the system. This isn't necessarily a common symptom, but it's possible. The air handler might also pick up a rattling sound from the outdoor condenser unit. If you hear the sound inside the house (near the air handler), go outside and listen to the condenser; if the sound is louder outside, you know it's not the air handler. You can try another trick with some (typically newer) systems: wait for the compressor to turn off at the end of a cycle, then listen to the air handler while it completes its cycle (this time delay doesn't occur with all systems or in all climates). If the blower is quiet while still running, it's off the suspect list.Ductwork SoundsNot to dash your hopes here, but ductwork is less likely to rattle than it is to rumble, boom or pop (caused by the thin duct metal expanding and contracting with changes in temperature or air pressure) or to whistle from the air itself.

That said, airflow can create a rattling sound at vent register or grill or even at a duct joint. If you think an air conditioner rattling sound is coming from the ductwork but you can't pinpoint the source, there's a good chance the rattle is being transmitted through the ducting from elsewhere in the system. Time to take another look at the air handler and condenser.Rattling Window UnitsSmall air conditioners, such as window and through-the-wall models, have the compressor and air handler systems in one unit, and no ductwork (unless you've tried to MacGuyver something here). electric furnace ac unitIt's common for compressors and fan motors on small units to become noisy over time as lubrication deteriorates and motor bearings wear out. ac split unit systemInternal parts typically are sealed and therefore not fixable, but it may be cost-effective to replace a worn fan motor. how much will a 3 ton ac unit cost

An air conditioner with a rattling sound could have a problem with one of the unit's two fans; there's one in the front and one in the back. Fan blades can come loose or damaged and strike or rub against the fan housing. Fan blades (and blower wheels) are common replacement parts. But before you think too seriously about internal repairs, make sure the air conditioner rattling sound isn't coming from a plastic louver vent or other cover part on the front of the unit (you've probably already checked for that).How to Quiet a Noisy Forced-Air System In this how-to video, This Old House plumbing and heating contractor Richard Trethewey makes peace with a raucous heating duct In this video, This Old House plumbing and heating contractor Richard Trethewey explains how to quiet a noisy forced-air system. 1. Mark center of start collars on the return and supply side of the heating duct.2. Cut holes in sheetmetal ducts using a drill fitted with a circle-cutting jig. 3. Attach start collars to duct with ¾-inch self-tapping sheetmetal screws.

4. Install bypass damper between the two start collars; fasten damper with sheetmetal screws. 5. Seal seams around start collars with foil tape.6. Adjust the counterbalance weight on bypass damper arm. 7 Turn on furnace to ensure bypass damper opens.See products and services for this episode Tools for Quieting a Noisy Forced-Air System Circle-cutting jig, used to cut round hole in metal ducts 2. 7-inch start collars 3. ¾-inch sheetmetal screws 4. Foil duct tape, used to seal seams in ductworkCapacitor Failure Symptoms are sometime harder to identify without the right tools and expertise. Capacitors can be found in several different sizes and shapes. There may be one or multiple capacitors included in your ac with regards to the design. While the most popular capacitors are the types found on circuit boards, the ones most associated with air conditioning will be the bigger capacitors that assist start and run your motors. There are several motors present in an conditioner and heater systems:

Compressor Motor Run Capacitor: Here is the most popular capacitor that fails. Most of the time these are duel capacitors, which means that there are 2 capacitors built into one. A duel capacitor will have three terminals on the top where a single capacitor will simply have two terminals on top. Outside Fan Motor Run Capacitor: That is the smaller capacitor found with or part of the Compressor Motor Capacitor. It helps start and run the outside fan that blows air through the outside coils. Indoor Blower Motor Run Capacitor: Similar to the outdoor fan motor capacitor, it is a small, single (two terminals) capacitor that will help start and run the indoor blower motor. Start Capacitor: Some models include an auxiliary start capacitor that helps jump start the motors. Most are found on the compressor. These are less common. Why do capacitors go bad When capacitors go south, they either go out entirely or they decline in strength. The decline is measured in the “capacitance” units called micro farads.

When the capacitors are produced, they are labeled with their specifications capacitance and a range +/- from the design capacitance. This range is the allowable operating range, usually labeled in a percentage range, for the capacitor. If the capacitor starts to fail, the capacitance measured will be outside of the labeled range. Sometimes these are difficult to find any symptoms unless you have the proper tools. Warning, there is a risk of severe shock, so do not try this at home. Diagnosing a bad capacitor If a capacitor goes out completely, or is severely out of its operating range, it may prevent the motor affiliated with it from running completely. If the compressor motor is not working, then the air conditioner will not cool. If the outside fan is not working the compressor may cause problems and will short cycle or cease working. If the indoor fan stops, you’ll find that there is no air blowing through the vents. For Quick, Honest and Affordable Service, call Alexander Heating and Air Conditioning