Author Topic: Any HVAC Members?  (Read 174 times)

Offline stokester

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Any HVAC Members?
« on: December 18, 2022, 11:03:47 AM »
Asking because the blower motor in my unit has started making a bit of noise at startup, like it is taking longer to get to speed.  Normally there is only the sound of the blower kicking on.  This had happened before but went away for a few months.

I checked the running capacitor, a 5uf and it reads 4.58uf.  Is this enough of a difference to give it a slow start?  Working with electronics, generally within 10% is OK but the capacitor itself lists +-6% tolerance.  It's easy enough to replace but 8.4% low does not seem like much.

Thanks
Nick
Nick
Yorktown, VA

Offline bonneyman

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Re: Any HVAC Members?
« Reply #1 on: December 18, 2022, 11:21:59 AM »
Hi Nick.

Motor problems are a large portion of HVAC malfunctions. Noise or slow star-up could be a weak capacitor. Static testing - where you disconnect the cap and test it separate from the system - doesn't always show a weakness. Better to do a dynamic test, with the cap in the system with voltage applied under load. (I only learned about this test procedure a few years before getting out of A/C. I don't feel like I cheated customers for all the prior years because swapping out a cap was really cheap, just to be certain). Several companies I worked for after closing my business had mandatory (static) testing of caps on all units we serviced. I would also do dynamic testing on many of those - and I found alot that failed the loaded test even though they seemed fine when static tested. (Accuracy is key - this is one job that really needs a digital test meter). Here's the procedure:

https://hvacrschool.com/wp-content/uploads/2017/06/How-To-Test-a-Run-Capacitor-Under-Load-1.pdf

Also beware that the + or - 6% is manufacturers imposed tolerances, not really application guides. They test a handful of caps out of every hundred and - if the rating they measure is with the 6% either way - they sell it. The insulation in modern caps is super thin, and go weak all the time under heat. You could install a say 60mfd cap, and it could really be 6-10% low (say 54-56 right out of the box) yet your motor NEEDS the 60. (That's what the engineers designed it for). Try to find a cap that is as close to the label rating as you can. Brands change all the time - I liked AmRad:
https://amradmanufacturing.com/

Check all the power wiring and switches supplying the motor. Low voltage can adversely affect start-up torque and overall performance.

Lastly, could be worn/bad bearings. If the blower motor is more than 5 years old - and hasn't been oiled - could be the bearings are giving out. I know most motors claim to be "permanently lubricated", but that's misleading. So long as the motor lasts past the warranty period the manufacturer is off the hook. Even "sealed bearing" motors can be opened up and lubed. I pop the end caps off ( the forum member selling the mini pry bars has the right idea for this!) to expose the sawdust gland reservoir and bearing and put 10 drops of my Supco/Turbine oil mixture in. I have had only one motor in 14 years go bad for bearings after lubing with my brew. And I even brought back a few motors that were stuck - but I got to them before the windings overheated and my mixture freed the bearings and they started spinning again. The Supco 88 oil additive is superb - been helping me save anything that uses mineral oil. I even put it in my old Toyota!
Here's the link about Supco:

https://supco.com/web/supco_live/products/S8.html

Long winded but hope this helps!

« Last Edit: December 18, 2022, 11:41:03 AM by bonneyman »

Offline stokester

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Re: Any HVAC Members?
« Reply #2 on: December 18, 2022, 11:50:38 AM »
Great info.

Makes perfect sense about the static vs dynamic test.  I'll probably just spend the $10 and get a new one which will eliminate one of the possibilities one way or the other.  I know the old time capacitor checkers would apply the working voltage to see if there is a breakdown while the newer testers can check for Equivalent Series Resistance (ESR) but it is usually false economy to check and replace a $.50 component in a radio.

My system is a Trane XR95 installed right at 12 years ago and has been flawless to this point.  It appears I would have to remove the blower assembly to get to the bearings for any lube, not sure I want to take out that control board and other pieces right now.  There is no odor or signs of excessive heat at this point or abnormal noise once it comes up to speed.

Thanks much.

Nick
Nick
Yorktown, VA

Offline bonneyman

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Re: Any HVAC Members?
« Reply #3 on: December 18, 2022, 12:00:24 PM »
No problem
 
Does that Trane have an ECM blower motor? If so, those have ball bearings, so basically bulletproof mechanically. Noise could be the blower wheel. My unit has a whine now on start-up - started about 4 months ago. I suspect the wheel but really don't want to tear the furnace apart in the winter just to check. Plus supply change issues with the warehouses not being able to get parts. Yikes!

Offline stokester

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Re: Any HVAC Members?
« Reply #4 on: December 18, 2022, 07:39:27 PM »
Had to look up ECM (electronically commutated motor) to find out what it is and to my knowledge mine does not have one.  Always learning!

This is the motor as best as I could get a picture.  Probably typical of what is used today, made in India but to give credit it has worked for over 12 years in coastal Virginia.

Nick
Yorktown, VA

Offline bonneyman

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Re: Any HVAC Members?
« Reply #5 on: December 18, 2022, 09:13:17 PM »
So sorry about that - I just automatically assume the abbreviations are common knowledge.

Looks like your motor is a newer standard style. I did notice more motors were coming out of India toward the end of my business. It lasting 12 years can't be a bad thing. Keep an eye on it and if the noise gets worse you can swap it out. Not too awfully difficult if you're mechanically inclined.