I live in the Central Florida area and I have a Carrier Heat Pump system.

We recently entered into a time of year when the thermostat will not turn the system on as frequently as it normally does in the hotter times of the summer. The system will run an cool for a while and then shuts off when the house reaches the set temperature. The system will sit in the off state for quite some time. After sitting like this, when the system first comes back on, I hear a rather loud grinding/jet like noise sound which appears to be coming from the area of the air handler. The sounds lasts for a few seconds and then stops. The system apears to cool normally after this noise occurs. The sound is a little hard to describe but it almost sounds like a jet plane flying over the house at a high altitude. The sound does not occur every time but when it does it happens after the system has been idle for an extended period of time.

A few days ago, I had my air conditioner repair company out to check the system. Of course we could not get the system to make the noise while the repair technician was present. He checked the system over, doing all of the normal things that are checked during a system tune-up. He could not find anything wrong. The sound still persists on an intermittent basis. What could this sound be and is it cause for ...»

3 Comments

JL Spring & Associates Richmond, VA

If your fan in the system is a centrifugal one, sounds like the bearings may be going and you probably have a sealed "squirrel cage" and just need the new cage. Oiling usually only prolongs the inevetable and the grinding noise always returns,,,Best to you, hope you find a great HVAC member/contractor here on HT that does biz in your area! Use the search posts link at the top of this page for HVAC Contractors John. JL

on Oct 23, 2011 · Like 0
John Orlando, FL

The noise happens whether the fan is already running or not. I have been told that it is most likely refrigerant noise caused by the compressor starting up after being idle for a while. My question is, what causes this and is it harmful to the system?

on Oct 24, 2011 · Like 0
Emperor cooling and heati... Covington, GA

My guess would also be refrigerant due to the noise you are describing. I will try to elaborate as best I can. The refrigerant pressure in the system becomes equal during off cycles but when it starts up you have a sudden rush of liquid refrigerant that surges through a restricted valve in the indoor coil. There are many factors that can effect the pressure of the refrigerant but the largest one is temperature. With the difference in outdoor and indoor temperature that you are now having ...»
it will effect the pressure and therefore the noises produced by the refrigerant. Think of blowing air out of your mouth, you breath out you get little to no noise. You force the air through a restriction (say you are trying to whistle) and you get a different noise. Same concept. The refrigerant can be the culprit of many noise such as gurgling, whistling and sounds of water rushing through lines. Furthermore the unit you listed has an txv or thermostatic expansion valve which will reduce or increase refrigerant flow as needed to perform more efficiently so the sounds can change due to the change in flow. None of this is anything to worry about and even if it is something like noise coming from the fan, I wouldn't worry about it until the fan quits. The bearings locking down on the fan will not hurt the rest of the system because there are safety switches that will activate to protect the system from damage. Hope this helps and is not too confusing.

on Oct 24, 2011 · Like 3

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I live in the Central Florida area and I have a Carrier Heat Pump system.

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