Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > HVAC

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools Search this Thread Display Modes
Old 06-12-2013, 05:59 PM   #1
Newbie
 
Join Date: Dec 2010
Posts: 14
Share |
Default

Lennox Furnace with 63K8901 circuit board behaving strangely


Hi guys, I just had an HVAC technician out to help me attempt to balance an existing system in my house to get more A/C up to the second floor.

As part of this, he noted that the yellow wire was not connected to the furnace circuit control board. We traced that back up to the splice with the compressor signal and the thermostat wires and found that again, the yellow wire was *not* connected there.

The reason we were looking at that is because he suggested that we set the multi-speed fan (capable of 5 speeds, I think) so that when in fan-only mode, we'd run at the lowest speed (and possibly keep this on most or all of the day when it's really hot), but then when the cooling demand kicked in, we'd switch to speed 3 or 4 out of 5, to really push the cold air up to the 2nd floor.

He assumed (which makes sense to me) that this wasn't going to work unless the furnace board could see the cooling demand (which, with the yellow wire disconnected couldn't be happening).

The problem came in once we hooked up that yellow wire ... after a bit of back and forth, eventually what I see happening is that while the thermostat properly puts 24VAC on the yellow wire (and the green wire also has 24VAC), the furnace will not behave normally. What usually happens is that the compressor is running, but the blower is not on! Then, I think if I drop the temperature so the cooling demand shuts off, the fan comes on!

If I leave the cooling demand off altogether, and everything's not running, the fan-only button toggle behaves as normal.

Also, if we return everything to how it was: remove the yellow wire, things go back to normal, *but*, I think the furnace board is only telling the blower to run at the speed indicated for fan only (this board [and the blower] has separate configurable speeds for heat, cool, & fan only -- I imagine that's fairly common, but don't have a ton of experience with HVAC).

So I'm not sure what's going on here. I don't know if something got slightly messed up as part of our testing this configuration change or what, but it seems highly suspicious to me that that yellow wire was not hooked up in the furnace. We've been in the house about 5 years and I'm pretty sure no one touched that since I've been here (the system is about 15 years old now -- it's a Lennox, with a control board model # 63K8901).

I just wanted to put this scenario out there and see if anyone thinks this could be caused by anything but a bad furnace board -- that was the conclusion my technician came to (and I agreed).

My current idea is to just try replacing that board (I'll tackle it myself, and buy the part myself, so if it works, the cost will be nice and low). Just want to make sure I've not skipped some sort of simple-ish diagnostic before I dig into replacing the board.

Also note: here's something that I swear is new; it's only happened once or twice in testing, but obviously I don't want to keep testing it for fear of damaging my heat exchanger. I noticed when I put a heat demand on, I hear the burners light up, but *again*, the blower does not run! I believe this is even happening now when that yellow wire is disconnected on the board. I know that was not happening before, because we've gone through 4 or 5 winters with the furnace and it's always been fine.

Also, I do not think this has anything to do with the blower ... *but*, I suppose if someone has that as an idea and has a test to try on it, I could.

tgice is offline   Reply With Quote
Old 06-12-2013, 06:10 PM   #2
Hvac Pro
 
Join Date: Nov 2008
Location: Winnipeg, Canada
Posts: 8,992
Default

Lennox Furnace with 63K8901 circuit board behaving strangely


Probably the fan relay to turn on the fan to high speed for cooling is shot and they knew it and disconnected the yellow wire which when calling for AC will tell that relay to switch from heat speed to cool (high speed). sounds like that relay is now hung up in a middle space and not allowing the fan to work for heat either. you need a new board. in LOTS of cases where I am we use the lowest speed for AC as our ducts are big and it works well and dehumidifies better.

cozyparts.com is a great place for Lennox stuff and honest.
need the complete model and serial # for them not just the part # as Lennox changes them often

__________________
"Cut it twice and it is still too short".

Last edited by yuri; 06-12-2013 at 06:13 PM.
yuri is offline   Reply With Quote
Old 06-12-2013, 06:37 PM   #3
Newbie
 
Join Date: Dec 2010
Posts: 14
Default

Lennox Furnace with 63K8901 circuit board behaving strangely


Thanks Yuri! Glad you think it's likely the board should be replaced. Do you have any experience with trying to de-solder the relay and replace, assuming I can get an exact replacement for that part?

Not a good idea? Unlikely to work or last?

I guess I could always try that first, and *then* do the board replacement if it doesn't work or continue to work (wait until I get both parts in first).
tgice is offline   Reply With Quote
Old 06-12-2013, 06:41 PM   #4
Hvac Pro
 
Join Date: Nov 2008
Location: Winnipeg, Canada
Posts: 8,992
Default

Lennox Furnace with 63K8901 circuit board behaving strangely


faulty relay is just my educated guess and actually there are 2 fan relays and the board is not that expensive. I don't recommend trying to replace those relays.
__________________
"Cut it twice and it is still too short".
yuri is offline   Reply With Quote
Old 06-21-2013, 01:03 PM   #5
Newbie
 
Join Date: Dec 2010
Posts: 14
Default

Lennox Furnace with 63K8901 circuit board behaving strangely


Yuri, thanks again for your response. I wanted to post back that I did do a full replace of the board. I actually used a
White Rodgers 21D83M-843 model # that claimed to be an exact replacement for my 63K8901.

So far all of my tests have come out well and I can have my Y wire hooked up now and still have the fan run!

The only trouble I really had with the install was mounting the new board (which was a bit taller than the old one) in different holes, etc. I ended up mounting this metal plate that came with the kit to the old furnace to make things work. That's what I spent most of the time on. I spent about 2.5 hours doing this work -- only probably 45m or so was pulling the old 1/4" connectors and then figuring out how to reconnect them.
tgice is offline   Reply With Quote
Reply

Tags
63k8901, blower board, lennox, problem


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Lennox g40uh replaced control board with 83m00 dpledge HVAC 2 03-30-2013 08:56 AM
Lennox Furnace G27M Series Unreliable operation: pressure switch or else? sheppard1977 HVAC 7 01-14-2013 05:42 PM
Rewiring furnace electrical circuit BlueBSH HVAC 4 09-21-2010 01:34 PM
New Cased Coil - Install to Furnace - PICTURES!! hartkem HVAC 39 11-18-2008 01:45 AM
Inducer fan assembly or inducer control circuit board failing realblonde94526 HVAC 3 05-12-2008 07:28 PM




Top of Page | View New Posts

Copyright © 2003-2014 Escalate Media. All Rights Reserved.