Carrier - fan constantly on, no power to oil primary control


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Old 02-12-13, 07:25 PM
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Carrier - fan constantly on, no power to oil primary control

Hi All,

My Carrier oil furnace is running the blower non-stop and not firing the ignition. I've turned the thermostat off and have also disconnected it. The always-on switch is off as well, yet the blower keeps running... Like the board is fried or a relay is broken.

Second issue (more importantly) is the oil control module isn't getting power. Thinking the oil control module was at fault, I replaced it with Honeywell R7284. This model has an LCD and it seems ther is no power on this either.

Both issues happened at the same time, when I was away this weekend.

No clicking can be heard from the furnace trying to ignite (probably bc the oil control module doesn't have power itself).

I don't see any fuses I can easily replace on the circuit board - time to replace the entire board?

Circuit board model Honeywell ST9103A 1036
Furnace model Carrier 58CLA

Thanks for reading and any advice you can offer.
 
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Old 02-12-13, 09:36 PM
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it sounds like a safety limit is open.

http://www.managemylife.com/mmh/lis_...L/L0801121.pdf

 
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Old 02-12-13, 09:45 PM
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Ah, indeed, it is what it is. I'll order the part tomorrow, next day shipping. Wife will be happy to have heat again... She might make me call a tech next time, though.
 
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Old 02-12-13, 09:55 PM
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well, typically you can reset a limit.............................. No need to necessarily order a part just yet. First you need to determine which limit is open if any.
 
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Old 02-12-13, 10:11 PM
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The limit should have reset automatically if it overheated since its been a couple of days. How could I manually reset it?
 
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Old 02-12-13, 10:25 PM
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some limits such as the blocked vent switch require a manual reset. These limits typically have a small red button in the middle of the terminals on the limit. You should have 1 to 3 limits on your system, did you follow the red wires from the control board as shown in the previous picture and find all the limits on your furnace?
 
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Old 02-12-13, 10:28 PM
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I found the high power limit. It ran inside my furnace and is a solid structure, about the size and color of a dime. No other limits were found.
 
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Old 02-12-13, 10:36 PM
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Have you measured voltage across it? Sometimes just removing a wire from the limit or cycling the power to the furnace is enough to reset a stuck limit if it is an auto reset limit.
 
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Old 02-13-13, 08:18 AM
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I ran the following tests:
1. Continuity on the sensor: passed
2. Voltage check across the leads from the board to the sensor: failed.

Seems the limit leads aren't getting power. Is it worthwhile to try to trace it back to see why it has no power?
 
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Old 02-13-13, 02:10 PM
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>



From the comment above, I'm supposing you are not getting 24 VAC to either side of the limit switch when the thermostat is calling for heat and the inducer motor is running. Is that right?


Use a voltmeter to see if the pressure switch has voltage to it and is closing.


With the inducer motor running, you should have 24 VAC to both sides of the pressure switch and both sides of the limit switch.
 
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Old 02-15-13, 10:26 AM
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You say you don't have a fuse on the circuit board? Even though on a carrier, once the fuse blows, the fan will come on and stay on until fuse is replaced. A blown fuse would also cut power to the controller.
 
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Old 02-25-13, 09:17 AM
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Got the fan circuit board, swapped it out and the problem was resolved.
 
 

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