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Old 07-13-2009, 02:08 PM   #1
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Lennox G20 Series - Bad blower board - or is it more?


Hi all,

New to the forum. Old hat DYI'er.

History:

While running AC the system reached temp and shut off correctly (presumed). Then it simply refused to start. I wanted a new thermostat anyway (for energy savings reasons) so I bought one and things started and worked fine ... for two days. Big smile.

Again, the system would not initiate. Opening the access to the HVAC blower et al. I found water. "Not good," I'm thinking! I end up blowing backward on the consensor line and immediately was rewarded with a quart of water. AT this point I believe I solved the water problem. Now, what has been the result of the water was my next task. I found the water skirted all system wire points yet possible pooled in the bottom item .. The air cleaner control box?? Still not sure, haven't opened it up. I went after the blower et. al. first.

Following the Lennox Flow chart provided I jumped wires (r & G, R & Y, etc) to learn that all systems (AC, blower, heat) would run (except the air cleaner lights didn't come on). However I could not successfully jump the wires at the Thermostat side. So indeed, a bad wire was found that had rubbed open near sheet metal. It is certainly worth mentioning that the wire did have water on it. I believe the water finalized the "shorts" in the system. But leading to a bad original thermostat??? Maybe the original thermostat wasn't bad. No worries, wanted a new one anyway.

I replaced the wire AND the thermostat again. It ran fine for a week. Yesterday it died again; or didn't start as the case is. I do doubt the air cleaner has been working. I'm not sure it ever has since I bought the house in 2003.

Current:

I DO have power going INTO the Blower circuit board (BCC2) and the "current" does get past the switch to the board. However. I am UNABLE to jump R&G etc and get running parts. It appears current isn't getting through the board. This is confirmed by the Lennox flow chart which reveals that I need a new Blower circuit board. An internet search revealed that I require the 48K98 (48K9801, 48K98-LB) as it replaces all BCC1-3 older boards such as mine.

Questons:

1. Do I need a board?

2. What have I missed? I'd hate to get the board only to plug it in and have it blow again. Is there another item I should know to check??

3. Could the Air cleaner box be creating any feedback blowing out a blower board?

Thanks for reading and responding. The item is in excess of $100 and I'd hate to buy a part only to plug it in again and watch it fry.

By the way. After finding water I did place a large fan to blow on the HVAC for a day. A near 100 degree day.

Thanks again,

Richard

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Old 07-13-2009, 08:10 PM   #2
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Lennox G20 Series - Bad blower board - or is it more?


I see lots have viewed this posting. Hopefully someone will reply.

Here's what else I've learned.

Tonight when I go home I'll look for a fuse on the Circuit board but I doubt it has one. If the fuse is bad, replace and hopefully smile.

I'll also check for continuity at the 24 volt side of the board to see if one of my transformers may be the problem. There is no current at them.

So it's looking like one of three things:

1. Fuse - please
2. Transformer
3. Board

It's starting to look less like a board????

We'll see.

Any advice?

Richard

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Old 07-13-2009, 08:20 PM   #3
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Lennox G20 Series - Bad blower board - or is it more?


See if there are test points (TP1, TP4, whatever) on the board. Then see if the manuf. will tell you what voltages you should be seeing on those points. I doubt they will give you a board schematic, and it would be of limited use anyway.

If you post the system schematic then the impedance looking into each connection that goes off the board can be calculated and if all are OK then the board, in theory, should not blow out.

This might take a while.

Last edited by Yoyizit; 07-13-2009 at 08:25 PM.
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Old 07-13-2009, 08:30 PM   #4
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Lennox G20 Series - Bad blower board - or is it more?


Thanks for responding to the post!

I'll see what depth my manual has when I get home tonight. Hopefully my meter is worth a darn too.

I'm hoping there is a board fuse and that it's fried.

Outside of that, I'm not sure which is less expensive, A step down transformer or a board.

Question:

If I transformer goes bad does it take out other parts as it goes? Could it be a transformer AND the fuse?

Looks like I'll be getting familiar with the schematic soon enough.

Richard
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Old 07-13-2009, 08:54 PM   #5
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Lennox G20 Series - Bad blower board - or is it more?


Quote:
Originally Posted by inn8pwr View Post
Thanks for responding to the post!

I'm hoping there is a board fuse and that it's fried.1

Outside of that, I'm not sure which is less expensive, A step down transformer or a board.2

Question:

If I transformer goes bad does it take out other parts as it goes?3

Looks like I'll be getting familiar with the schematic soon enough.

Richard
1 That is just one possible beginning indicator
2 The board may be 10x to 20x the cost of a 'former.
3 upstream parts, usually.
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Old 07-13-2009, 08:57 PM   #6
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Lennox G20 Series - Bad blower board - or is it more?


Trans don't normally go bad with out cause, Chances are you have a blown fuse.
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Old 07-13-2009, 10:04 PM   #7
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Lennox G20 Series - Bad blower board - or is it more?


No fuse present. At least not on the board.

What now Mr. Wizards???

I'll likely take the board off and look for board issues. I'm starting to doubt that I'll find any.

This DIY'er is about to call for help... beyond this forum. Dern, they just charge to show up.

Thanks for continued help. Please show me which path to follow.

Richard
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Old 07-13-2009, 11:05 PM   #8
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Lennox G20 Series - Bad blower board - or is it more?


You ;;;,p,;
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Last edited by hvaclover; 07-13-2009 at 11:08 PM.
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Old 07-14-2009, 01:28 AM   #9
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Lennox G20 Series - Bad blower board - or is it more?


Not quite sure what to make of your last posting.

I am still attempting to DYI, just not getting anywhere.

Latest find was NO on board fuse.

Continued problem: no current on the 24 volt side of the board.

Likely problem?? Perhaps my water problem effected the transformer??

I have been active attempting to locate a circuit board should it come to that. I've sent my make and model number to a parts house that is looking it up.

I'll atempt to examine the board as well.

But I am still asking this forum what the best course of action is??

I suppose I need to learn how to test a transformer.

Thanks for reading and responding, ...... constructively.

Richard
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Old 07-14-2009, 12:19 PM   #10
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Lennox G20 Series - Bad blower board - or is it more?


Quote:
Originally Posted by inn8pwr View Post
Continued problem: no current on the 24 volt side of the board.
I guess you mean no voltage. If you have a clamp-on ammeter you could check if the 'former secondary is shorted by something on the board, which means the secondary current should be quite a few amps and the 'former won't last much longer.
Also check that the 'former primary is getting its rated voltage, probably 120v.

A 'former with an open circuited secondary should read ~27v. It reads 24v when it's loaded down with its rated current. A 40 VA 'former would have a rated current of 40/24 = ~1.7A.

Post a photo of the board.
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Old 07-14-2009, 11:18 PM   #11
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Lennox G20 Series - Bad blower board - or is it more?


You won't find a fuse on that G-20. However if you look around the outside of the electrical box you should find a little square black and white button. This is a resettable breaker that is used instead of a fuse. If it is tripped you have shorted the stat wires somewhere.
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Old 07-14-2009, 11:21 PM   #12
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Lennox G20 Series - Bad blower board - or is it more?


That's what I was trying to remember.

Damn WhisperHeat.
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Old 07-15-2009, 06:25 PM   #13
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Lennox G20 Series - Bad blower board - or is it more?


Hi all,

Thanks Skip, you are correct, there is no on board fuse. At the site you suggested I did previous fine a seperate switch with a screw-in type glass topped fuse. The fuse remains fine and I do have 120V going into the board.

However, I have found that I do not have 24V coming out of the Transformer. The 24V side is "open" and I just brought home a replacement one.

Prior to installing and powering up I'm in a hunt to find the cause of the Transformer blow-up?? I have chased the line to the AC and fine it free of fraying.

Not sure what to do now and am considering hooking it all up and see how long the transformer works.

So here's the question:

Would a problem on the board cause a transformer to blow???

If so, I suppose I'd better test the board as previously posted, or replace the board.

Would a bad board blow a transformer??

Thanks,

Richard
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Old 07-15-2009, 06:36 PM   #14
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Lennox G20 Series - Bad blower board - or is it more?


Fuse the secondary of your new 'former.
For 40 VA at 24v you could use 40/24 = ~1.5A slow blow.
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Old 07-15-2009, 07:02 PM   #15
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Lennox G20 Series - Bad blower board - or is it more?


Nice.

So are these in line fuses??

BTW:

I went ahead and put her back together and the house is cooling as we speak.

Thanks for the help. Looks like I can avoid the expense of a blower board for now.

I will look into the 40V/24V inline fuses.... if you meant inline.

Thanks,

Richard

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