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Ducaticorse 05-02-2010 03:51 PM

Bryant Plus 90 - No Blower
First post, already with a question! :laughing: Hoping that the DIY crew can help either confirm my diagnosis or send me on to look at a few more things.

Equipment: Bryant Plus 90
Model: 350MAV048100
Control Board: HK42FZ011
Age: ~13yrs / 1997?

Situation: We have a 2-story home and quite often keep our fan set to "On" rather than "Auto" to help keep the temp upstairs somewhere in line with the temp downstairs, always tends to be colder up there in the winter, warmer in the summer. I came home from work on Friday and found the house to be a bit stuffy, so I went to the thermostat and flipped the blower to "on." In Michigan this time of year, we haven't yet fired the A/C - usually just circulating the air on a warm spring day is plenty.

After switching on the blower, I realized that it was quiet - blower not running. No blower or inducer blower, from what I could tell, whether demanding cool or heat. In heat, no action at all, simple as that. In cool, the outside compressor kicks on, and I can hear the circulation in the A/C lines but the blower never spins up.

Diagnoses so far: I hopped on the computer and started searching/reading. My initial fear was that the blower itself had failed. I also came across some info suggesting that a wonky thermostat could cause such problems as well. So:
  • Main Blower OK - I connected the "Cool" blower lead to the downstream-side of the door switch and voila - blower. Nice and quiet, no drama or noise - just a quick, smooth spool-up.
  • Thermostat OK - Dug out my old original thermostat from many years ago and connected it. Same phenomena, no blower but compressor kicks on outside when demand for cool.
  • Control Board Fuse OK - Visually good, Fluke says continuity OK
  • Control Board Test NOK - I connected a test lead to the Test terminal on the control board and clipped it to C/24v. The LED simply flashes at a fast rate. No inducer blower kick-in nor the follow-on sequences. No code, just constantly flashing fast, I gave up counting at 25 fast blinks in a row... :laughing:
  • Inducer Motor Spins Freely - A quick check shows that the armature of the inducer blower motor and the blower itself spin freely by hand. Very smooth, no apparent issues like a stuck armature or blower blockage.
  • No (apparent) shorts, bare wires, double checked all connections - I unplugged and plugged all main board connections to try to rule out a connectivity problem. Looks OK?
My first-time DIY furnace diagnosis suggests that I need to swap out the control board. I can't see an easy way to quick-check the inducer blower to "hotwire" it like I did the main blower, otherwise I'd check that as well just to be sure.

From info I've read here and elsewhere, I need a 325878-751 "conversion" board to service this. I have downloaded a .pdf of the instructions for that kit, looks pretty straightforward.

Seem like a sound diagnosis? I'm not sure exactly what to make of the failed control board test, except possibly to confirm my suspicion that there's something failed or amiss with the board itself. None of the troubleshooting info I can find suggests next-steps when a constant fast flash is returned.

I currently have the blower bypassed to the door switch as it's been pretty warm the past few days here. I have no problem taking on the control board swap, just looking to some experienced eyes to look over what I've done to avoid a mis-diagnosis or unnecessary board swap.

Thanks for any help or guidance! :thumbsup:

yuri 05-02-2010 05:39 PM

The board is bad, has a history of failing due to weak solder joints. I have replaced dozens of them. Average life on any circuit board is 10 yrs. Be VERY careful how you connect the flat pin adaptor cable onto the new board. One shot only, break a pin and it is toast!

Ducaticorse 05-02-2010 05:46 PM

Thanks for the confirmation, yuri! I will definitely be careful on the install.

It is so cool to be able to learn about this sort of stuff via the web with online resources like this one!

yuri 05-02-2010 05:50 PM

Yeah, if I could just get some "helpful" lottery ticket choosing techniques I could do this fulltime.:yes:

clpearson 05-07-2010 12:12 PM

Wow, this is amazing. I have a very similar problem with my Bryant.

My uncle is an HVAC tech and had diagnosed the control board as the problem. My question is how did you find out about the conversion board and the part number? He has left me in charge of ordering the part as he's very busy, and said he'd return to install it. I don't even know where to start looking for that information! I tried googling the make and model which led me here.

If you could point me in the right direction I'd be very thankful.

Bryant Plus 90
Model # 350MAL036060

Thank you so much,

Ducaticorse 05-08-2010 01:08 PM

Christine, I google searched like you did and came across info that provided me with the part number I needed to use. Some searching should provide you with the same kind of info. You should be able to see the existing control board number on the top of the board itself. My control board had a black plastic-like cover over many of the components, and there was a decal on that cover with the number: HK42FZ011 When I searched this number I found that there was an upgrade/replacement board that was to be used.

However, when I search 350MAL on your behalf, I don't find any reference to this model? Can you confirm that this is the right model number? Or maybe Yuri or one of the other pros here can help?

yuri 05-08-2010 01:50 PM

You need to find that HK number as there is a whole series of them from -008 to -018 etc and you need to make sure the conversion kit is correct for your unit.

bkelly65 06-17-2010 01:52 PM

This thread may be dead already but I wanted to thank you guys. I had a similar problem with a UT HK42FZ011 board. After reading your descriptions, I isolated and verified the blower - ok. Then I pulled the board. The descriptions that I read indicated that bad solder joints are a chronic problem with these. Bad solder joints on the larger "discrete" components usually don't cause damage to the component itself - just to the connections (land) on the board. the damaged area was obvious to see and was in a predictable spot - on one of the relay pins where the power to the blower fan is switched. This connection would normally heat up a lot from switching such a large power device. The connection area was burned away from the relay pin. I scraped a little varnish off of the conecting land a little further down and soldered a bare wire from the relay pin to the exposed area (approx 1/4"), plugged it up and away it went. The board fix is easy for anyone who knows how to solder. Considering the age of the entire system, I didn't think it was worth a replacement board. Thanks again.

NitroNate 06-17-2010 02:03 PM

had a similar problem with my furnace a couple of years back. took the control board out, flipped it over, saw a visibly burnt out solder joint, re-soldered it, put it back in, voila!!

control boards can easily be soldered with a $10 radio shack iron. it's been running fine ever since and it saved me a couple hundred bucks to replace the board.

Good 05-12-2011 02:29 AM

Amazing - Problem Solved
It worked like a charm! I had the same problem - No Blower. Found the burnt terminal on the back of the board exactly as described. Fluxed and re-soldered it! The blower now works and all is well! Saved hundreds! Thankful for this forum and the shared experience and advice! Still amazed!

The Help 03-05-2012 10:41 AM

The Fix ! It works
Same problem, try it, and it now WORKS!! No Blower. Found the burnt terminal on the back of the board exactly as described. Fluxed and re-soldered it! The blower now works and all is well. :thumbup:

TinkerTailor 10-16-2012 08:39 PM

Saw this forum the other day after searching for my controller part number. Same problem, and same solution - just a little solder on the back of the board and I was back in business! $200 in parts saved! Don't want to guess labor charges :)

medinapool 01-01-2015 07:56 PM

no blower and horrible smell
I am still diagnosing but it appears to be the controller. I just wanted to mention the awefull smell we had, to a point we had the fire dept show up. Smell radiated through out the house.

wallybob 01-03-2015 04:39 PM

Thank the Almighty for you guys! I had the same exact problem with my Bryant 90 furnace and it turned out to be a worn out PCB solder joint on the blower relay connection just like you said. I was talking to the repair guy on the phone and he just laughed when I asked him how much a new control board was going to cost and said "you don't want to know..." Thanks a million - I joined this forum just so I could give you guys a shout out!

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