Author Topic: HVAC Issue with electrical burning smell  (Read 773 times)

chops

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HVAC Issue with electrical burning smell
« on: August 22, 2017, 01:27:00 PM »
We have a 1995 G20 Lennox Whisper Heat HVAC unit, lived in the house for 2 years, worked fine since we moved in.  We don't use the central air often, (We're big fans of the fans!) but our premie newborn came home from the NICU this week and we were told we should keep it cooler for him so I turned on the HVAC central air...and I got nothing.  No air movement from the HVAC blower fan, just a buzzing sound.  Also an odd burning smell (electrical-ish?) was evident around the inside hvac unit.  The outside unit was spinning fine.

I looked up some common issues and it seemed that the capacitor or the transformer can cause these symptoms so I replaced them both.  Now if I turn on the HVAC A/C I still get the buzzing sound and no air flow...BUT if I push the blower fan with a pen it will start up and work fine.  No burning smell anymore.  I am now thinking it is a control panel issue so I looked at that best I could but couldn't see any burned marks on it which I read usually indicates an issue. 

Any thoughts?

Thanks!

 - Chops

BlueMR2

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Re: HVAC Issue with electrical burning smell
« Reply #1 on: August 22, 2017, 04:17:09 PM »
Sounds like a failed blower motor to me.

chops

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Re: HVAC Issue with electrical burning smell
« Reply #2 on: August 22, 2017, 07:46:11 PM »
Thanks BlueMR2 - so you are thinking it could be a failed blower motor even though it works fine after I give it a helping push with a pen? 


GuitarBrian

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Re: HVAC Issue with electrical burning smell
« Reply #3 on: August 22, 2017, 11:13:32 PM »
Sounds like a bad blower motor. Or capacitor.
Don't let the motor overheat.
I think you have a 60L21 blower motor. (Quick Google search YMMV)
Look up your model number and learn how to test the Capacitor and wiring. Sometimes there isn't info specific to your unit, so try Lennox air handler blower motor test or something like that.
If both check out... Cap is within 10% and wiring is showing good voltage. Then replace the motor.

BlueMR2

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Re: HVAC Issue with electrical burning smell
« Reply #4 on: August 24, 2017, 05:33:41 PM »
Thanks BlueMR2 - so you are thinking it could be a failed blower motor even though it works fine after I give it a helping push with a pen?

That's how my blower motor failed.  It couldn't start anymore on its own, required a push start.  When not able to run it'd sit there buzzing and generating an ozone smell.  My ceiling fan died the same way too...

BudgetSlasher

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Re: HVAC Issue with electrical burning smell
« Reply #5 on: August 25, 2017, 05:39:39 PM »
Which capacitor did you replace? PSC style motors (which are what most HVAC blower motors are) have a starter capacitor attached to them; this capacitor, as I understand in, essentially knock a bit of current out of phase and provides the initial magnetic field that is required to get the motor started. It is not uncommon for these to fail (though it is not that common either). This would explain your issue. These capacitors are usually strapped to the side of the motor and your specific motor will determine the spec of the capacitor you need. (Had this issue when we moved into this house)

Another issue could be the bearings, most HVAC blower motors have bearing on the shaft that are meant to be oiled, but almost never are. There will be little holes at the front and/or back of the housing that should face up (and if you are lucky still have the little plastic plugs in them). Sometime a sticky bearing can stop a fan from starting, but once the friction is overcome they run fine. I recommend a "zoom spout" oiler (look on amazon) to help you reach the ports.

Finally the motor could just be failing, our limped along with oiling the bearings, but ultimately failed. A new PSC blower motor is around 90 dollars on amazon (or at least our was), but there are more expensive, and efficient ECM retrofit motor that can be purchased as well. 

Kroaler

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Re: HVAC Issue with electrical burning smell
« Reply #6 on: August 28, 2017, 04:51:55 PM »
If you can start it with a stick it's the capacitor most likely.  Check it with a digital meter.    If it's not that it's something in the start circuit.    But those symptoms really scream capacitor.    Being able to push it into starting is usually the give away. Again unless the winding the capacitor feeds (the out of phase one) is burned up.    Either way you can check both of those with a meter.   (Safety first, don't do anything if you don't know how)

chops

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Re: HVAC Issue with electrical burning smell
« Reply #7 on: August 30, 2017, 01:56:59 PM »
Thanks all for the input!

I changed the start capacitor and still just getting the buzzing sound...unless I push the blower fan, that still will get it started.

Kroaler, I'll check the winding the capacitor feeds with a meter, maybe that's it

otherwise it sounds like a new blower motor after all.  Anyone know if I have to replace the motor with the exact one (60L21, thanks GuitarBrian) or can I use a generic replacement that has similar dimensions, hp, etc?

Thanks again,

Chops

 - Chops

Agg97

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Re: HVAC Issue with electrical burning smell
« Reply #8 on: August 30, 2017, 03:13:31 PM »
Anyone know if I have to replace the motor with the exact one (60L21, thanks GuitarBrian) or can I use a generic replacement that has similar dimensions, hp, etc?

I would get an exact replacement if possible.  With the generic ones (also known as "universal" ones), I've had issues with getting the right adapters to attach the motor to my blower housing; also, wire lengths are sometimes an issue.  Finally, the fan speed RPMs might not match on the universal ones.  With the money you're saving by DIY, it's worth a few extra dollars to get the exact one, IMHO. 

With that being said, I ended up putting a universal one in when my blower motor went out.  That was what the supply house had in stock, and the wife and kiddos didn't want to wait for the OEM part to come in.  However, the fan speed was only 1075 RPM instead of 1130.  It is noticeable how much slower the squirrel cage sounds and how much longer the unit runs even with that small of a change.  But, there are bigger things on my "honey do" list than to replace that motor, so I've just kept it.
« Last Edit: August 30, 2017, 03:47:25 PM by Agg97 »

Kroaler

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Re: HVAC Issue with electrical burning smell
« Reply #9 on: September 03, 2017, 04:44:03 PM »
How deep do you want to go with troubleshooting vs just throwing parts at it?

https://www.amazon.com/gp/aw/d/B00NWGZ4XC/ref=mp_s_a_1_1?ie=UTF8&qid=1504477496&sr=8-1&pi=AC_SX236_SY340_FMwebp_QL65&keywords=clamp+on+amp+meter&dpPl=1&dpID=41sQt%2B0%2B-SL&ref=plSrch

Can you safely use a meter?    Some interesting thoughts I have. 

You changed capacitor and it didn't start, but you can start it with a stick.   The problem is still somewhere in the start circuit.     Your motor is stuck in between 2 magnetic phases that are 180 degrees out.   That's where the start circuit comes in.    It gives a little starter magnetic field about 90 degrees out.    Once rotation begins the start field is no longer needed since the momentum and phase change allow it to go from 1 field to the next field.   That's why you can poke it with a stick and it takes off, your doing the job of the start circuit.   

Obviously the motor isn't locked up or it wouldn't spin, however if you want to check the health of the main windings and bearings, you can check the amperage (with a clamp on meter like linked) .     The motor plate will have an FLA value for full load amperage.   Your amperage should be very close to this value.  If it is over, there is some sort of mechanical resistance or winding failure.         However I don't think that check is needed....

Something is stopping your start circuit from developing a magnetic field.   If you changed the capacitor that is possibly ruled out.  The only true way to rule out capacitor is to find a digital meter with capacitor check and check the old one, that's the 100% check.   

The next thing to do is disconnect the motor start circuit windings and ohm the windings for the start circuit.  Some digging around online should provide the desired measurements.  It would be in a field service guide for your unit.     If the windings are good, and the capacitor is good, there is something not turning on like a relay or bad connection in my opinion.

But I imagine you've already resolved the problem by now since it's hot out.       If it was me, I would set my thermostat to a value so cold it can never get there, start the thing by hand and let it run constant without cutting off untill you have good time to dick with it lol.

chops

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Re: HVAC Issue with electrical burning smell
« Reply #10 on: September 06, 2017, 12:30:55 PM »
Thanks again all.  I still am waiting on the replacement blower to come in.

Kroaler, I will try to troubleshoot the old motor when I have a chance.  I'm not schooled yet in using a meter but will youtube it and try to learn.

When you say it may be a "bad relay or bad connection" do you mean between the control panel and the motor or in the old motor itself?

Thanks!

- chops

Kroaler

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Re: HVAC Issue with electrical burning smell
« Reply #11 on: September 07, 2017, 06:00:42 AM »
Not inside the motor.    Somewhere in the control circuit.   

Will be interesting to see what you find when the old motor is able to be bench tested.