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We moved into a house with a 12 year old goodman (Xenon brand but I was told goodman parts) and two end bells on the furnace fan motor have burned out now (I know from the old owners receipts it happened before). The folks who repaired can't tell me why...that I seem to have a lemon. I use MERV 11 filters, have the furnace cleaned annually and vents cleaned last year. Any thoughts on what might cause this and anything I could look into so we don't have this happen again. @chris mentions airflow potentially...how do I know if Adjustments are needed? Also, I read that the newer furnace filters MERV 11 and under have good airflow...is there a way to test my system for airflow and how the filter way to affecting this? I can easily change air filters if that is this is the consensus though. I don't know if this means anything or not, but we also have water dripping out of the air return during the air conditioning season...I thought I heard repairman say that fan speed could be adjusted to fix this...any ideas?enter image description here

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    What model is this, and are you talking about a bearing burning out, or something else? – ThreePhaseEel Dec 19 '16 at 3:50
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    I wonder if someone "opened up" the ductwork so that you are moving more air than designed, and drawing more current - in general overloading the motor. It's a common error when someone who does not truly understand starts messing with the system balancing dampers. – Ecnerwal Dec 19 '16 at 3:58
  • To clarify, it is an ECM motor and I saw (and smelled) the end bell when it burned out. I will certainly ask my repair man about decreasing the aurflow setting if you think that is a concern...no one has mentioned this. – Moni Dec 20 '16 at 0:37
  • You can't/shouldn't decrease the airflow setting, as that would mean not enough air is passing over the heating element or burner. That would decrease efficiency and risk damaging another part. You MUST decrease the amount of work the motor has to do by using a higher-airflow filter, as suggested by @chris. – pbarranis Dec 20 '16 at 1:01
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It sounds like you have an ECM "constant flow" blower that ramps up output as high as necessary to maintain the set airflow (aka an ECM constant torque motor). A MERV 11 filter is too restrictive for most residential systems. In this case, the motor would compensate for the restrictive filter by running harder and hotter to maintain the airflow. Switch to a MERV 8 filter (it's still a pretty good filter). If your system delivers more airflow than you need, then also set the airflow selector switches in the furnace to a lower setting. Obviously the air filter should also be changed regularly before it becomes plugged or the blower will again ramp up to a very high level to compensate.

EDIT; Specifics related to OP's situation:

It turns out OP has a very high performance MERV 11 filter which if correctly matched to the system might be OK. The stamp on the side of the filter states "Airflow Capacity up to 1400 CFM." In reality I would expect this to mean this filter might be successfully employed on a system with a 3 ton cooling capacity (3 tons / 1200 cfm). It would not work for a larger system.

I found more detailed information on an air cleaner that uses OP's media here:

http://www.cleancomfort.com/assets/Brochures_SpecSheets/Filtration/SS-AM11-3225.pdf

The referenced unit above uses two (2) AMP-M1-1056 filters and therefore handles twice the airflow of OP's setup. In my experience a pleated filter is near its end of life when the static pressure drop reaches about 0.2" WC. Looking at the "AM11-3225-5 Pressure Drop vs. Air Flow Rate" chart on page 2, one sees 0.2" static pressure loss corresponds to 2600 CFM for two filter cartridges when new. So according to this chart, 1300 CFM would be the max airflow through OP's one cartridge when new and if one were to run the filter at that high a flow it would need to be changed very frequently (at least monthly?) because it would become more restrictive as it filled with particles.

My conclusion: If OP's system does not exceed 3 tons / 1200 CFM and OP changes the filters monthly (normal intervals of 3-6 months are plausible if the system is 2 tons / 800 CFM or smaller) then the existing setup is probably OK. Otherwise switch to something less restrictive.

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  • Just to chime in, this is exactly right. Your filter is the problem. I have been scolded by two different HVAC guys due to wanting to go above a MERV 8 in a residential system. Two dogs... dust by the pound... you get the idea. Let some air move through your system and use a filter with better flow. – pbarranis Dec 20 '16 at 1:02
  • We use Aprilaire No. 201 pleated paper filter elements which supposedly have a MERV 10 rating, but the blower motor in our middle quality Carrier HVAC has lasted 24 years. I suppose it has a standard motor rather than an ECM constant torque. Some of these innovations have unexpected negative consequences. – Jim Stewart Dec 20 '16 at 15:49
  • So, I asked my repair guy to bring a lower MERV rating filter and he said the fan didn't burn out, the end bell that controls the voltage on the fan burned. So, any ideas? Still the filter? Thanks – Moni Dec 23 '16 at 23:09
  • The end bell is more of a variable speed drive and not just a voltage control. It is cooled by the airflow moved by the fan and it does operate hotter when the fan is used to move air against a restriction. High heat kills electronics faster than windings. Mystery to me why the repair guy is balking at this concept. Yes I still think a MERV 8 fitler is the correct choice along with setting the blower airflow lower if your duct work permits that. Here's a youtube url on basic ECM motor construction: youtube.com/watch?v=5Q5mm1Nqx9U – user39367 Dec 24 '16 at 5:00
  • BTW, not all "MERV 8" filters are equivalent. The MERV rating measures the particle size removed and not the restrictiveness of the filter per-se. In general a MERV 8 is somewhat restrictive and a MERV 11 is significantly more restrictive, but there are "high capacity" MERV 8 filters that are less restrictive than standard MERV 8 filters. They have more surface area (higher pleat count). Also, 2" pleated filters are typically less restrictive than 1" pleated filters if a system accepts 2" thickness. A 2" pleated standard capacity MERV 8 is my usual selection. – user39367 Dec 24 '16 at 5:10

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