Coleman troubleshooting help needed - http://www.hvacmechanic.com/ Forums
Original message
| TimS
 |  "Coleman troubleshooting help needed"
, posted Sat 23 Oct 16:06:  
My Coleman BGU (70% eff, home unit - not mobile) furnace won't light, when I attempted for the first time of the season.
The board would just hum when called for heat. The blower will run when switched to AC, and the fan position at "ON" or with the AC running. I took the old board out, and found burned contacts on what appears to be the heat relay. I unsoldered the heat and AC relays and swapped them and reinstalled the board. Same result. The board gave not flash codes either time.
Next, I bought a new board. The board kit contains a new style board and all necessary wiring harness adaptors. I wired it up per the instructions, and the SAME RESULT. Just a hum from the board (a relay I assume) and no blower, no light, etc. The board is flashing a code for stuck upen pressure switch. I took the pressure switch out to inspect it. The diaphragm moves freely, and the limit switch works too, checking for continuity with a DMM. I switched the leads on board for the blower motor for heat and cool, and the blower will still run when the thermstat is switched to AC and the fan in the "ON" position. So, I assume the wiring is OK back to the blower motor.
One other question, the old board had one lead going back to the blower motor labeled L1. The new board doesn't have that label, rather two different "park" terminals. I attached the old L1 lead to the "park" inline with the "heat" terminal.
On the new board the Limit switch is wired in parallel with the pressure switch. Perhaps this is the culprit? What reading should I get across it with the furnace off? Open or Closed? If closed is there a specific resistance range?
Thanks,
Tim.
[this message was edited by TimS on Sat 23 Oct 16:40] |
| Replies:
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| Mastertech
| "Re(1):Coleman troubleshooting help needed" , posted Sun 24 Oct 12:38
I think u said that the code was pressure switch closed before draft motor came on. Which indicates the control board will not bring on draft motor until circuit is fixed. Think u said u had a parrallel circuit with high limit switch and pressure switch.
That cant be, it must be in sereis.
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| TimS
| "Re(1):Coleman troubleshooting help needed" , posted Sat 23 Oct 16:42
Where I stated L1 above, should have been M1.
Thanks in advance for any help,
Tim
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| | Mastertech
| "Re(2):Coleman troubleshooting help needed" , posted Sat 23 Oct 17:51
Long time no hear lol. For the pressure switch not in use should be open circuit. As of limit and pressure switch being in parrallel that cant be right because most boards check to see if pressure switch is open then turn on draft induced motor.
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| | Mastertech
| "Re(3):Coleman troubleshooting help needed" , posted Sat 23 Oct 17:55
The hum u hear is that just the Transformer?
Or is that the draft motor?
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| | Mastertech
| "Re(4):Coleman troubleshooting help needed" , posted Sat 23 Oct 18:06
As to the blower conection - goes something like this.
4 wire to blower
1) Black to cool on board
2) Blue to heat on board
3) white to common on board(Cir)
4) all the rest got to park(just as the name implies no action)
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| | TimS
| "Re(5):Coleman troubleshooting help needed" , posted Sun 24 Oct 01:39
The hum is the transformer. The draft motor isn't starting, I suppose thats my problem.
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| | Mastertech
| "Re(6):Coleman troubleshooting help needed" , posted Sun 24 Oct 01:47
Did u recheck the pressure switch wiring?
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| | TimS
| "Re(7):Coleman troubleshooting help needed" , posted Sun 24 Oct 10:43
I checked the pressure switch wiring. It tested OK.
The sequence of events for start-up is
1. Start ID fan?
2. Open gas valve/ Ignite?
3. Start of blower motor?
Is this correct? If so, my ID fan is not starting. I've removed it to inspect the motor. As of now I can't get the set screw out of the fan impeller locking collar so I can seperate the motor from the fan housing. Using MAPP gas and liquid wrench!
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| | xenos
Webmaster 
| "Re(8):Coleman troubleshooting help needed" , posted Sun 24 Oct 13:36
Yes that fan does need to start first.
Xenos.
The best way to escape a problem is to solve it.
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| | TimS
| "Re(9):Coleman troubleshooting help needed" , posted Sun 24 Oct 14:54
I've pretty much destroyed the ID blower assembly/motor trying to get it apart. Apparently, moisture has reached the assembly (presumably down the stack) rusting it all together.
I heated up the set screw on the collar trying to get it to break loose, twice. I got it too hot and it burned the grease out of the motor bearings.
Next, I took the dremel to the collar and cut half of it away. The collar still won't come off of the motor shaft! Amazing. If I manage to get it apart, I'll try greasing or replacing the motor bearings and giving it another shot.
Some good news though. You guys were right about the limit switch, it is wired in series with the pressure switch. I switched the leads to the pressure switch and gave it a whirl (with the ID fan disconnected) just to see. The blower motor started! If I ever get the ID replaced, I'll be back in business. Other good news is that it's warm enough here today not to need the furnace!
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| | TimS
| "Re(10):Coleman troubleshooting help needed" , posted Sun 24 Oct 20:32
Anyone know of good national or internet source for a AO Smith 961 (catalog 150, page 91)ID fan assembly? My local supplier doesn't list it in their online catalog.
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| | Mastertech
| "Re(2):Re(10):Coleman troubleshooting help nee" , posted Sun 24 Oct 21:02
Need to find a coleman dealer to get that part.
But might get lucky johnstone.
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| | Mastertech
| "Re(3):Re(10):Coleman troubleshooting help nee" , posted Sun 24 Oct 22:00:
I think its time to call a tech in before u cost yourself alot of money.
If u use the heater alot and cost alot to run(its a 70% very ineffecient) before fixing i would get a price both for fixing and replacing.
Some times tough love is the only way.
[this message was edited by Mastertech on Sun 24 Oct 22:04] |
| | TimS
| "Re(3):Re(10):Coleman troubleshooting help nee" , posted Sun 24 Oct 21:44:
The local Johnstone doesn't have it in their online catalog.
[this message was edited by TimS on Sun 24 Oct 21:45] |
| | TimS
| "Re(4):Re(10):Coleman troubleshooting help nee" , posted Sun 24 Oct 22:46
I've spoke with some in the business, and based on my current usage and billing, there's really not adequate payback to justify a new one.
If I can buy this darn motor for a decent price, I'll consider myself lucky. Your right about calling in a professional though, I shoulda done that about a week a half ago!
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