My furnace unit started making a squealing sound today. Does anyone know what this is? Anything I can fix myself?

Maybe related, the temp was high 90s today and the AC was actually behind. I have it set at 76 and it was at 78 early this afternoon and still hasn't shut off yet, 6 hours later. Secondary question, should it be behind or is that another issue?

It squeals for 2-3 minutes, then is silent for probably 2-3 minutes.

Video: https://youtu.be/yWVDllF5rrc

EDIT: Is this where the oil goes, this black tube? enter image description here

  • 1
    Narrow down the issue to the fan or the A/C by turning the A/C off, and just running the fan only. Do you still hear the noise from ONLY the fan?
    – Freiheit
    Commented Aug 12, 2016 at 15:03
  • Added a picture of the motor. Is that black tube for oil?
    – rys
    Commented Aug 12, 2016 at 18:44
  • Seems like it could be the oil port, but without the model number, I can't be sure.
    – Tester101
    Commented Aug 12, 2016 at 19:51
  • I can't find it without removing it, dangit. Looked all over no yellow or red caps. Furnace is 1990 carrier
    – rys
    Commented Aug 12, 2016 at 20:01
  • Reluctantly spent $90 for technician to come oil the motor. It still squeaked after he left so set up time for furnace replacement. A couple days later the fan stalled completely. That gave me courage to inspect it myself. I removed the blower fan and motor. I also disassembled the motor until I had the issue narrowed down to one bearing. Turns out he did not oil it. The bearing closest to the fan was bone dry. I used 1 whole ounce of oil to fill the 2 oil ports (one on each side of the motor). The hole underneath the black tube in the picture is the oil port. Furnace is working great again.
    – rys
    Commented Aug 21, 2016 at 13:08

2 Answers 2


If the blower in the furnace is belt driven (not likely), the belt might be worn and slipping. Most likely, the blower is direct drive, which means you'll probably have to pull out the entire blower assembly to get at the motor.


  • Before removing the blower, make sure power to the unit is OFF.
  • If you have to remove wiring to pull out the blower assembly, make sure you label each wire so you know where it goes.

Once you have the blower out and accessible, you should be able to locate the two oil ports. These ports are typically on the "top" of the motor, and are plugged with plastic or metal caps. Remove the caps, fill it up with oil, and replace the caps. Check the manufacturer's documentation for the type, and amount of oil to use.

Here's a good YouTube video from Grayfurnaceman that shows How to oil the HVAC fan motor.

If the motor in your unit does not have oil ports, you might have to replace the bearings, motor, or the entire blower assembly (depending on which unit you have).

As always, if you don't feel comfortable doing this type of work, please contact a local licensed HVAC technician.

  • Great video. Can I get that oil at general/retail store? I'll have to take another look at the furnace to see if I feel comfortable doing it myself. Thanks.
    – rys
    Commented Aug 12, 2016 at 14:55
  • Looks like Walmart sells it, not sure if they have it in store. Might have to go to a local HVAC supplier to get it.
    – Tester101
    Commented Aug 12, 2016 at 15:11
  • Thanks looks online only. Would 3 in 1 work? Also, I attached an image to my question. Is that black tube for oil?
    – rys
    Commented Aug 12, 2016 at 17:24
  • Nevermind, found some zoom! But still not sure if that black tube is for oil. Any ideas? Picture attached above.
    – rys
    Commented Aug 12, 2016 at 18:03

I listened to the UTube,,, could not hear what you described. With a audible noise on the condensing / compressor unit, I have found the problem to be the bearings in the fan. Some 3/1 oil or WD40 in the bearings close to the motor shaft of the fan may help. If this helps the grease in the bearings has dried out and the oil may give a few more years of life. After this the bearings in the fan motor will need to be replaced / or the motor itself. Since you have an oil port a few drops of automotive oil would work well.

  • Please don't use WD-40 as a lubricant. Also note that the equipment in the video appears to be a furnace, not a condensing unit.
    – Tester101
    Commented Aug 12, 2016 at 11:09
  • @tester101 both 3 in 1 oil and WD 40 work well to help small bearings that have dried out. Both can add years to a bad "small load motor" . I looked at the video again and on my phone it is hard to tell but it looks like the furnace or air handler on the evaporator so I agree with that.
    – Ed Beal
    Commented Aug 12, 2016 at 13:11
  • Did you have the volume turned up? :) Yes, it is a furnace.
    – rys
    Commented Aug 12, 2016 at 14:52
  • @EdBeal WD-40 works well at collecting dust and debris, not so well as a lubricant.
    – Tester101
    Commented Aug 12, 2016 at 14:58
  • diy.stackexchange.com/questions/6226/…
    – Freiheit
    Commented Aug 12, 2016 at 17:46

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