[cagefighter]

I woke up this morning full of Christmas cheer and then I noticed it was too cold (I have compromised with my wife to turn the heat down to 65 degrees at night, but not 60! Brrr!)

I noticed the circuit breaker was tripped so I reset that. The circulation blower comes on but no ignition or heat. The White Rodgers 50A50-471 control board was blinking 3 times meaning "problems with pressure switch".

Now it gets interesting... I overrode the pressure switch and thereby fooled the control board (it started blinking in "call for heat" sequence). After a 30 second delay or so I got ignition (then I realized it is not a good idea to override safety switches, when I singed a few hairs on my hand). But the draft induction motor did not come on no matter what I did, which is why the pressure switch would not close.

I opened up the White Rodgers control board and found a big burned spot right by the plug to the induction motor. But remember, I said that the board seemed to be working fine except that the induction motor would not turn on. I have included pictures.

[IMG] Motor+Board+#2.JPG (image) [/IMG]

[IMG] Motor+Board+#1.JPG (image) [/IMG]

My dilemma is this: what caused the burnout and circuit breaker trip, the motor or the control board? If I replace the board (~$100) which otherwise seems to be working and then find that the motor is bad, I will just burn up another board. If I replace the motor (~$200) and it still doesn't work, then I know the board is bad and I just bought an unneeded motor.

Any ideas?

[hvac1000]

Look at induction motor is 115/120 volt then just apply power to the motor only and see if it spins up. Test cord work well in this case.

You can solder over the joints just to see what happens.

[wmproop]

Either way looks like board has bit the dust,, you could run power to the induction motor from another source to see if motor is/will run

[MarkwithaK]

Your best bet is to bite the bullet and replace both now. Even if you replace the board and the motor does start, chances are that there is some internal damage and the motor is not long for this world.

[KISS]

Good speculation. The contacts in the relays failed.

The motor may be drawing too much current or the relays failed due to use. You really need to measure the current draw of the motor outside of the ckt board and compare with nameplate. Only then can you determine if the motor is bad.

The age of the furnace might help us guess.

You can always play and replace the relays and bridge the foils and clean them up, but I suspect you need heat.

[cagefighter]

The furnace is about 11 years old.

Where are the relays located? The wires run directly from the control board plug to the motor.

I like the idea of testing the motor independently. I think I can modify an extension cord with some alligator clips to make a test cable. I do not have an ammeter, however, and we just got a lot of snow yesterday so I don't think I'm making it to Sears today as I can't even get out of my street to go to work.

I would like to know if the motor is bad before I go any further.

[KC13]

Test - run the motor as previously instructed. It is possible that the solder joints on the circuit board melted out with age, oxidation, and subsequent heat build-up. I have seen this occur many times on many different type of systems. Look for evidence of arcing between the board and nearest grounded metal surface. An improperly installed board can fall victim to ground-contact failure.

[KISS]

The Aromat black things are relays. They fail. 11 years is good life. Good life for a furnace too.

Now the bad news: Aromat was gobbled up by panasonic and there has been recent initiative to reduce hazardous substances such as Cadmium. They may have 24 VDC or AC coils. It's more likely to be DC.

They look obsolete just looking up the part number.

Now the fun part, obtain one through excess inventory and you'll spend $300 per line item. Get one surplus and your lucky.

Hopefully the manufacturer didn't obsolete the parts as well.

Your Christmas list may have just changed.

[KC13]

If the OEM replacement for this board will force you to refinance your mortgage, you may consider a universal replacement. Usually less costly, but you'll probably want to have a pro install it.

[hvac1000]

The universal replacement is nice. Comes with jump connectors so you might not mess up.

http://www.white-rodgers.com/wrdhom/..._50a55_843.pdf


New one on Ebay

White-Rodgers 50A55-843 Universal Integrated Fan Board - eBay (item 120316257092 end time Jan-08-09 04:05:14 PST)

[cagefighter]

Look for evidence of arcing between the board and nearest grounded metal surface. An improperly installed board can fall victim to ground-contact failure.

Good call. A closer inspection revealed a big black spot on the furnace housing right where the board was installed. What could cause it to spontaneously fail like that after 11 years of working just fine. It has been colder than usual around here for the last two weeks. Maybe the more frequent duty calls finally got to it?

Could the failure of the relays that KeepItSimple suggests have resulted in the arcing? Does that help me get any closer to determining the root cause, motor or board?

I'm leaning towards just replacing the old board with the suggested replacement from White-Rodgers which the website says is universal:

http://www.white-rodgers.com/wrdhom/..._06_pg0066.pdf

I'm going to try to test the motor, but if that is inconclusive, I will just take my chances and hook the new board up and hope for the best. Do you really think I need a professional to connect the wires (I marked them all before disconnecting them) and mount the board?

[KC13]

Arcing will look like a welder hit it. Blackening may just be from a release of Magic Smoke near that surface. Assure that the new board is properly and securely spaced from the mounting surface.

[hvac1000]

The kit might wire somewhat different than the old board. Get the board and take a look to see if you feel like you can do it.

[KC13]

Excellent point. Read the instructions BEFORE releasing any more Magic Smoke.

[cagefighter]

The replacement control board is on order, now I just need to convince my wife that we are saving money by waiting 2-7 business days for it to arrive so I can install it.

(Actually, we have a gas fireplace and a few space heaters going and it has been plenty warm.)

I may need some help in a few days when I try to install it.

[KC13]

You are definitely saving money. Overnight shipping is expensive!

[cagefighter]

Okay. Bad news...

Because of all the snow and delays of UPS deliveries in Western Washington where we live, my new control board didn't come until a few days ago. I went to install it today and carefully connected all of the wires just like they were on the old control board.

I flipped the circuit breaker on and about 2-3 seconds later it tripped again. When I flipped it again, the "internal failure" light came on and held solid on the control board for a few seconds and then tripped off again. I took the board off and there is no evidence of anything burned up nor any smell. The fuse on the board is not blown.

Could it be that the board was bad to begin with? Shouldn't the fuse protect the board from burning up like that? What could be drawing so much current that the breaker is tripping?

I tested the induction motor by just spinning the rotor and it spins very freely (i.e. bearings are fine).

Help me someone... I'm confused and my wife wants a working furnace. Should I call a repairman and fork out the big bucks for a professional? That sounds expensive...

[hvac1000]

If what you got was a brand new board then the failure rate out of the box is almost nil like in nothing. As mentioned before you have to follow the directions that came with the new board period.

Your quote

I went to install it today and carefully connected all of the wires just like they were on the old control board.
The old board and this new one could have some different wiring or switch settings.

Now with all that said there has to be a big power used or short to cause the internal failure light to come on and trip the circuit breaker.
MAKE sure the 120 volt feed is correct. That the hot and neutral are on the correct contacts on the board. Disconnect all furnace main blower wiring so the board will be bare except for the minimal wiring. This way the board is somewhat isolated.

Disconnect all other wiring on the board except the power feed. NOTE make sure you identify the wires so you know where they go. Then turn on breaker again and see exactly what happens.

Is the internal failure comes on again then I would feel the board itself has a problem.

You stated that you had checked the inducer motor with a jump cord as you were instructed to do so that should not be a problem.

Your quote

The furnace is about 11 years old.

Where are the relays located? The wires run directly from the control board plug to the motor.

I like the idea of testing the motor independently. I think I can modify an extension cord with some alligator clips to make a test cable. I do not have an ammeter, however, and we just got a lot of snow yesterday so I don't think I'm making it to Sears today as I can't even get out of my street to go to work

KC13 reply

Test - run the motor as previously instructed. It is possible that the solder joints on the circuit board melted out with age, oxidation, and subsequent heat build-up. I have seen this occur many times on many different type of systems. Look for evidence of arcing between the board and nearest grounded metal surface. An improperly installed board can fall victim to ground-contact failure.

NOTE:

If you never did test that inducer motor like you were supposed to now is the time and it may be too late.

Testing the inducer motor by spinning the rotor with your fingers is not testing the inducer.

[cagefighter]

Hanks hvac1000.

I followed your advice and I progressively reconnected components to the new board until the board was telling me that it had a pressure switch problem (3 blinks) just like before with the old board.

I went and bought a multimeter at Sears and found that I have 0.4 ohms of resistance across the motor. So I guess I found my short... it was the motor all along. But the old board does look pretty bad so it is probably a good idea to replace it anyway.

I took the old induction fan motor off and I have found the following online:
https://keithspecialty.com/k/68-509.htm

Do you think it will be very hard to install by myself? The old one wasn't too hard to take off. Any tips?

[hvac1000]

That says it is a two stage unit.

Post your brand and EXACT model number for your furnace