Questions & answers about how to diagnose loud start, popping, rattling, rumbling, running water sounds or just plain silence at an air conditioner or heat pump.

This air conditioning repair article series discusses the diagnosis and repair of air conditioning compressor noises which range in importance from normal (if annoying squeaks and squeals, to rattling loose bolts and hardware, to costly compressor damage indicating air conditioning compressor or A/C compressors at or near end of their life.

HVAC Noise Group 4 Q&A on loud start, popping, rattling, rumbling, running water sounds at an air conditioner or heat pump.

Also "no noise" or "silent" equipment

These questions & answers about popping, rattling, roaring or rumbling noises from HVAC systems such as air conditioners, AC compressors, or heating furnaces were posted originally

at HVAC NOISE-4 POP, RATTLE, ROAR, RUMBLE - be sure to see the diagnostic suggestions given there.

Article Index

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New AC unit making rumbling noise when running.

New AC unit installed recently and I have several concerns. We went from 3 to 3.5 ton after a heat load showed a need for 3.2 (they said to round up). 3 ton lasted 20 years but was failing so we went ahead and replaced. The unit cools well but when it is running, it makes a low roaring sound audible throughout the house. It's particularly bothersome at night.

The technicians have come twice to turn down the fan speed to reduce noise and add a baffle and ductboard to the return area to try to quiet it. The unit is condensing on the inside of the closet and even with the blower on low, it still blows so hard that it shifts papers around and really dries out your eyes due to the wind in the house. I just checked and the attic isn't properly sealed from the closet.

I'm concerned that the unit is oversized. Any advice? It's only a week old!! Home is 1450 square feet, located in south MS. I timed the cycles and when set at 77, it runs 6 minutes on and 10 minutes off. The company basically just said that was the noise it was going to make. I feel like we need a 3 ton, but I was assured this was the size needed to move enough air around our home. Could it be something else? Poor seal? Ductwork, return size, supply register size? On 2019-06-25 by New AC

by (mod) - when to go to your A/C equipment manufacturer or dealer for help with odd equipment noises

There are two questions here for which you need information and help from the manufacturer.

1. The first is whether or not the system is oversized.
2. The second is whether or not the noise you hear is normal for that particular brand and model.

Those are not things I can answer with no other information about you or equipment or building or duct work or installation.

But you can get help from the manufacturer or from a trained service technician.

Mini chiller A/C system vibrates loudly when the compressor starts

I have a mini chiller system with scroll compressor,it runs and makes cool well but when the compressor wants to start, it starts loudly with vibration for around 5 seconds.

When i checked the compressor I saw it's sweated, wet and cold under the suction line.

System is clean and when i checked the suction pressure it shows a little undercharge and when i want to add gas i see no change in pressure.Do you have any idea? On 2019-05-31 by Mori

by (mod) -

The compressor may be having trouble starting against head pressure. That would not be a low refrigerant problem. It could be a problem with a expansion valve or cap tube that is sticking or clogged.

by Mori

The device for expansion looks like a blud canister.

by (mod) -

Mori

The blue canister , if that's the item to which you are referring, is a filter drier, not a refrigerant metering device.

by Mori

Thank you Dan

I think a service tech might check the high side pressure at the time that the motor is attempting to start.

What do you suggest to do

Reply & Suggestions by (mod) -

Mori

The service tech will check the high and low side refrigerant pressures and check the current draw as the compressor is starting: those data points can help determine if the compressor is in trouble or if the problem is elsewhere.

What's causing a loud rumblingat our Trane XB-10 air conditioner and should we turn it off?

We have a Trane XB-10 air conditioner outside, our furnace and duct work are in the attic.

Our Furnace worked fine all winter. We have not used it for a couple weeks and today turned our AC on for the first time.

We got a loud rumble (my husband thought it was our neighbor starting up his motorcycle) from the attic, I believe the noise was from the fan as the AC sounded OK.

Should I leave the AC running and see if it stops or have a technician come out and look at it? On 2018-04-07 by Shirley C

Answer by (mod) -

Shirley

Watch out: Because there could be electrical or fire safety concerns, if this is a new noise and not one that's always been there as the system has been in use before, I would turn OFF the system and call for repair.

The issue could be simply a loose fan belt or blower component but it'd be safest to have a technician take a look.

Let us know what you're told as that will assist other readers.

Water source heat pump making rattles like stones - only in cooling mode

My water source heat pump makes a rattling sound (like stones bouncing around) when in cooling mode. It does not do this in heating mode or fan only mode. It just seems to be present during the cooling cycle. Any suggestions ? On 2017-06-17 by Ken

by (mod) -

Sorry to say I would leave that system turned off, since if the problem is an overpressure condition of refrigerant the system is unsafe. It's time to call for a service tech.

The reason you hear this only in cooling mode may point to a problem with the compressor or with the reversing valve that switches refrigerant flow direction between heating and cooling modes.

A/C unit makes firecracker popping noise and smells like fire and is sparking: What doI do?

Popcorn or popping sound like a firecracker on startup accompanied by sparks and smell of fire. What could this be? On 2017-06-06 by Katlynn

by (mod) - turn the system off immediately

Katlynn

Watch out: If you haven't done so, leave the equipment you are describing turned OFF IMMEDIATELY since sparks and smell of fire risk an actual fire or shock injury.

It's time to call for repair. I cannot diagnose your equipment from just your one line e-text but it certainly sounds as if there is an electrical short circuit or overheating motor or component.

The system is unsafe.

There's a Very loud scary pop when heat is turned on - repairman says it's a gas pilot light issue

Very loud scary pop when heat turned on, then no sound and no heat. Paid repair man 2 days ago that said it was pilot light or thermostat On 2016-12-09 by J jackson

by (mod) - warning about unsfae gas heater

J

Sounds very odd to me but of course I can't be as smart as the service tech who is on-site.

A thermostat is a low-voltage switch that turns heat or or off. I'm unaware of what would POP loudly in that device.

A pilot light, suddenly igniting a collected quantity of gas could cause a pop or bang or explosion.

If that is happening your heating system is very unsafe - there may be a gas leak or a defective gas control.

Watch out: The risk is fire or explosion. I would ask the repair person for details about exactly what was found as a problem and what repairs were performed.

Is it ok to turn on heat if the indoor air handler is vibrating?

My inside unit vibrate when I turn it on an it didn't do that before my friend say something is stop up an I was wondering can I turn on the heat On 2016-10-23 by Don

by Mod

Don,

From just your text I cannot of course know what parts are vibrating. Minor vibration may not be serious.

But a fan who's bearings are failing or fan belt that's breaking could cause costly damage to the air handler.

What might cause Tapping noise at a Carrier AC unit

I have a 6 month old hvac system carrier.

Today I heard a rapid tapping inside the furnace likely the expansion valve as it seems to be on the high pressure line.

After turning the system off, the tapping continued for a couple min then stopped. I waited an hour or so and ran the system again and no tapping sound. Any ideas? On 2016-09-03 by greg

Answer by (mod) -

Ideas yes you bet. Knowledge. No. Guesses:

Most common: tapping or clicking caused by a loose squirrel cage fan blower rotor or a fan blade hitting an obstruction .

Other sources of tapping noise:

Dirt or debris but also ice can cause the thermostatic expansion valve TEV to chatter.

Dirt and debris accumulate. Ice melts, and probably forms again later depending on conditions.

See CLICKING SOUNDS from air conditioner or heat pump system - also see FAN NOISES, HVAC - including ticking - also see HVAC TICKING NOISE DIAGNOSIS

Lennox AC unit is making a helicopter noise - is this normal

Lenex out side unit of heat pump making like a helicopter noise.

Had two heating people look at it and tell me it is normal. I installed the unit eleven years ago and never had this noise. On 2016-08-20 by Anonymous

by (mod) -

The fact that the noise is new on an 11 year old unit is certainly suggestive that something has changed. "Normal" is sometimes true and sometimes, IMO, shorthand for "I've no idea but this sounds like more trouble than I want to deal with".

See if you can determine if the noise is coming from

- the fan

- the compressor motor

- loose parts

- a relay or control board

What causes at rumbling rattling noise at a Split AC unit

Hello, I have a 1 ton split ac unit which I bought 2 months back. It not used much.

In recent days when I turn on the system, the outdoor unit makes a rumbling and rattling noise like a trunk in wrong gear!!

After 5-10 seconds it becomes silent and works well. This problem arises only when I turn on the system after a long break of time ( more than 24 hours) if I turn off the system and turn in on after few hours it starts without any unwanted sounds...

Im wondering if there is some problem with the piping and refrigerant or valves or capacitor?. the chance of bad motor is ruled out as it runs like a charm after that initial rattling start up..

I'm just wondering what would be the problem and how serious it can be ? Can it pose problems in long term? Should I call a technician asap? Thanks in advance On 2016-07-29 by Balaji

by (mod) -

Balaji

If you're sure that the noise is not simply loose parts, I'd ask for help from a service tech who might want to check the refrigerant charge.

I worry that liquid refrigerant is entering the compressor - if so that will ultimately damage it.

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Continue reading at HVAC NOISE-4 POP, RATTLE, ROAR, RUMBLE - loud start, popping, rattling, roaring, rumbling, running water, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

HVAC Noise Diagnosis Articles

• NOISES, HVAC SYSTEM DIAGNOSIS - home
• NOISES, HVAC SOUND DESCRIPTIONS - Index to all noises & sounds
• HVAC NOISE-1 BANG BUZZ VIBRATE - banging, bearings, buzzing, thumping
• HVAC NOISE-2 CHATTER CHIRP CLANK FAN GROAN - chatter, chirp, clank, clunk, cyclical sounds, fan noise, groan, growl, gurgle
• HVAC NOISE-3 HISS HOWL HUFF HUM - hiss, howl, huff, hum, groan, woo wuu wuff or humming noises
• HVAC NOISE-4 POP, RATTLE, ROAR, RUMBLE - loud start, popping, rattling, roaring, rumbling, running water
  • LOUD NOISE at STARTUP then quiet HVAC equipment
  • POPPING or POPCORN noises - turn off the system immediately
  • RATTLING & vibration noises from A/C or Heat Pump System
  • ROARING NOISE from A/C Compressor/Condenser unit
  • RUMBLING NOISES A/C compressor/condenser or blower fan motor noise
  • REFRIGERANT PIPING NOISE - running water or gurgling sounds, sounds in refrigerant piping - floodback or condensate? [Separate article]
• HVAC NOISE-5 SCREAM SING TRUMPET WHINE WUWU - scream, sing, squeal, trumpet, water sounds, whine, whoosh, whistle, wuwuwu, or silence
• SOUNDS of RUNNING / DRIPPING WATER in DRAINS - for running water sounds traced to a building plumbing drain system

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INDEX to RELATED ARTICLES: ARTICLE INDEX to BUILDING NOISE DIAGNOSIS

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