I have a Tappan (Nordyne) furnace with a variable speed blower motor (and dual stage burners). The Blower Motor will not run and the error codes off the Blower Motor Control Board is telling me that there's a "Motor Fault." How can I determine if the Control Board is bad also? The Blower Motor is DC Voltage. Model. # is: Tappan FG7TC 100D-VC. The unit is about 12 yrs old and I had to replace the blower motor once already in 2011. These blower motors are about $500 without the control board o it seems pretty ridiculous to replace it every 10 yrs.

Thanks for any input

 

It's probably the module that's bad, not the motor.

If the motor is non-communicating you can test for signal to make sure the wiring harness and main control board are good. Need a multi-meter. I believe it's versions below 3.0 that can be tested like that.
Can also make sure the controller is getting power.

The controller can be removed from the motor and winding ohmed out. You can give the motor a spin to make sure the bearings are good.

If you're loosing modules, your air ducts are probably undersized for the furnace.

Possible it's just a bad thermister on the motor's controller and that's field replaceable if you can solder.

 

Does your motor/module have a data connection with many pins/wires? If yes, it's not ecm 3.0+.

 

Motor troubleshooting info - http://www.munchsupply.com/media/ass...g_Tech_Tip.pdf

 

T
hanks. So the control board only gets power when the A/C is running? How many volts would I check for at the ECM? I’ve read that it’s more likely that the ECM goes bad and not the motor

 

I am getting 120 volts AC going to the motor. Where does the voltage get reduced to the 24V? Does that happen in the motor housing?

 

I found the problem, it's the Control Module.


Now I just have to find out where to buy one! I'm in Buffalo, NY. Any ideas???

 

Just to answer a few of your question...
The 120v to the motor should be always on.
24vAC is sent to the module to select speed or mode.

I don't see a replacement module listed for that motor.

 

Thanks PJMax & user 10. Any idea where I can find a Thermistor? The one I need is an: NTC 1D-25. I’m in Buffalo, NY

 

Two online retail sources.........
Allied
Newark

 

No luck with those two but thanks just the same PJMax!

 

A static pressure test should be done after the repair.

Could be undersized ducts and or filter (1" pleated bad for bigger furnaces) doing it. Minor changes may yield major reductions in pressure.

 

Whoops..... my bad.

You need a 1 ohm 12A 25mm NTC thermistor.
You can buy them directly on ebay from china distributors. Probably take several weeks.

I found a Honeywell 1 ohm 30A but it is a 32mm in size. Slightly larger........ Allied

Possibly similar part. Honeywell 1 ohm 30A in 30mm size....... Mouser

This part looks almost identical. It's 1 ohm 11.5A and is 15mm in size..... Digikey & Mouser

 

This is crazy! What do the pro's do? I can't find the parts anywhere and that's using an account. My buddy found a complete blower motor assembly for $550 and that's under his account. I tried to find just the Control Module but no luck. I found a local supplier that is bringing one in to Buffalo, Ny from Chicago and it's supposedly $350 so we'll see. The thing that kills me is that this is all because of a burned out Thermistor. I can't seem to find the Thermistor either. Does everyone go through this?

 

You need a new module, the circuit board itself is damaged, there's no use in just changing the thermister. If you change the thermister, you'll probably have future problems.

 

Thanks user 10. Where might I find a Control Module? This stuff is impossible to find.

 

Very hard to find due to having proprietary programming and most brick and mortar suppliers only selling to contractors.

You'll have to find the suppliers (mostly online) that will sell to the public and contact them to see if they sell programmed modulate for your particular furnace.

 

That's a Broad Ocean 622448 basic replacement motor.
I have not found a module for it and being what it is...... I doubt they'd sell a board for it.

 

The complete furnace model number can be used to source the part.

Also, if the existing motor is ecm 3.0+, there is a drop in generic replacement which takes it's programming from the control board. Not cheap but less costly than oem motor + module. i doubt yours is though

https://www.regalbeloit.com/brands/G...green-VS-Motor

Advertised to replace ecm 2, but requires a separate module which costs money and commissioning - avoid that.

 

Well, I got the new motor yesterday and it's up & running! I found the Thermistor on eBay so I'll fix the board on my old motor and use it as a spare. It's crazy, the motor varied in price from $350 (what I paid) to $600!

It's just frustrating because I put in (what I thought was) a good system. When I put it in in 2008, it was a pretty common unit around here (Western New York). And the blowermotor failed once before in 2011 when this unit was only 3 years old. I really wouldn't think anything of it if these motors were cheap, but at this price, it's crazy! For one thing I couldn't find one anywhere local, also they were as much as $600! I found one at a distributor for $350 but I ordered it Tuesday and it didn't get here until Friday! The other crazy thing is, this is the cost with me doing it myself. Luckily, the guy I do some work with is an HVAC guy so he has an account, so those prices are at a discounted cost.

I researched the ECM motors and their lifespan is 90,000 hours which is about 10 years. My last one lasted 9 years. Is this what everyone goes through? I remember AC blower motors lasting 20+ years. In another forum they were saying maybe it's some other issue that's causing them to go bad. Any other ideas???

Thanks!

 

Some don't last that long. These ECM motors run hot and that doesn't help to extend their life.

Welcome to energy saving motors. They save you on running costs but cost more to repair.

 

What kills these motors/modules is having ducts that are too small for the equipment.

The module ramps up the blower above the typical rpm to deliver proper airflow, and in doing so current draw increases exponentially- the electronics get cooked. Newer ecm motors do a better job of limiting speed/current draw by limiting airflow at high duct pressure so they're less likely to kill themselves trying to get proper airflow.

Your model number suggests it's 100 000 btu/hr which is huge for a residential furnace. Unless you have a very large or poorly insulated house, it's probably oversized.

The duct static pressure should be checked. If you're using a 16x25x1 pleated filter, it's far too restrictive for that furnace - that style/size is only good for 60 to 70k max. (90%+ efficiency assumed)

It should be noted that while AC psc motors last longer when the ducts are undersized, they don't move enough air, so the heat exchanger overheats and cracks prematurely instead.

Either way, undersized air ducts kill modern furnaces.

Part of the problem is that some contractors match the BTU input to what's there even if the old furnace is 60 to 70% efficient. They ignore the fact that more of the heat produced stays in the house and new furnaces need 50% more airflow relative to capacity. Between the two, required airflow can almost double!

 

The main advantages of the variable speed: range and direct static pressure compensation.

Not worth it for energy savings but now a more basic ecm is required to comply with regulations - such a shame.

 

Thanks for all the info! My house is 2400 sq ft. The furnace I replaced was a 165,000 btu, I put in a 100,000 btu. So, I'm not thinking it's oversized. Is the only way to test the airflow issue with a Static Pressure test? I actually consulted a guy I knew on the sizing before installed it. I never did a Static Pressure test though since I installed it myself. I've watched contractors though, and it seems to me that most of them don't even do a Static Pressure test before or after an install unless you're going with a big $$$ company. So the Static Pressure should be checked before & after the filter & A-Coil? If it's off from what the install manual dictates, what needs to be done?

 

Static pressure/airflow testing is part of the commissioning process. Along with other things like gas pressure, combustion testing, current draw and such.
You still could have a grossly oversized unit, as sizing isn’t done via square footage.

 

If detached 2-story with insulation, doubt you need more than a 80k at 95%+ - though roughneck is right, load calc required.

Oversized or not there's a high chance the ducts are too small or there's some kind of bottleneck which took out the module.

What kind of filter do you have? Are you running it on a 2-stage t-stat so the high fire is kept off unless it's brutally cold or u raise the temp up?