What does a high pitch noise coming from my central air system mean?

Question

Usually in th evening when the thermostat is turned down to 70 degrees fahrenheit for the night, our central hot/cool air system makes a high pitch noise. It is not constant; it lasts for several minutes; and it has no pattern in its occurance. My neighbor said this happened to her for a few years in her home before it eventually stopped working and needed to be fixed. My problem has occurred for approximately 2 years or so. The system does a good job of cooling our 4 bedroom home, but I'm concerned about its longevity. Any advice will be greatly appreciated. Thank you much!

Answer 1

sometimes you'll hear that during high energy usage times.  strange but true.  and not just your air conditioner but the tv, radio, etc......

Answer 2

It is probably your evaporator valve. this is the valve that joins the high pressure side of freon from your compressor to the low pressure side through the evaporator (the expansion of freon from high side to low side gives you the cooling in the coils which air then flows over.) Over time oxidation can start blocking this valve and it "whistles" until enough cold freon flows through.

Your neighbor is right - over time you can get a chunk that blocks this valve then it needs to be replaced and the system recharged.

No telling when, or if, this would happen to you though.

Make sure the high pitch isn't coming from the compressor (the thing outside with the big fan). If it is, it could be a bearing or a compressor that's failing and that definately needs to be looked at.

A tip  - call your local electrical union or votech school. They often like to come out and take a look at stuff like this to train their students. They typically will charge you nothing, or very limited, for the labor and the parts will be discounted. (They do appreciate soda and chips while they work, though! As Most service folks!). It could cut your repair bill by a lot. BUT, they obviously don't do "emergency repairs" or warranty their work so it's not a replacement for knowing the local AC guy.

Stay Cool!

Answer 3

Central Air systems should be inspected and given maintenance every 2 years, just like your furnace.  Call someone in your area who is HVAC certified to come service it.

Answer 4

dear kristen, i'm sure you'll find all these answers entertaining and some have merit, most are way off base !!  if the sound is more of a squealing noise of couple of those answers may be close,, if its a weird whistling sound then it is a hole in the duct work maybe a misaligned duct!!  the unit pulls and pushes air thru the duct,, any hole will cause a whistling as the air is rushed thru it!!  there could also be an obstruction in the vent acting like the reed on a clarinet with the wind again!!

Answer 5

It is probably a bearing that is causing it. Might be the circulation fan. Get it checked out (Possible fire)! Better safe than sorry!

Answer 6

It's hard to say without hearing it but it could be the compressor relief valve going off on high pressure. This would be an extreme case of a dirty outdoor condenser coil elevating pressures to the point were it would do that.

If it's a slight pitch change it may have to do with the expansion device that regulates the flow of refrigerant into the evaporator coil.

The valve will regulate itself to the load of the air passing over the coil.

This may be normal.

In any case a maintenance checkup by a qualified person will put your mind to rest.

Answer 7

It may be the blower or squirrel cage needs oil or new bearings and a good cleaning might be in order as well. shut it off some morning, unplug it and slide it out and take it out side and clean it, use a water hose a brush or two and a product called Simply Green degreaser. TSP and hot water works great and is allot cheaper.