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Old 09-17-2013, 03:57 PM   #16
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Something keeps running on A/C


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Originally Posted by firedawgsatx View Post
What I suggest is that you turn the power off to the furnace, set the thermostat to OFF and then turn the power back on to the furnace. Then see if code 21 is flashing? Code 21 indicates the main gas valve relay (MGVR) or 2-stage furnace control is stuck closed or there is a miswire or short to gas valve wiring. Try the suggested step and let us know if the code clears.
I had the power off to the furnace with the thermostat set to off when I replaced the circuit board. As soon as I switched on the circuit breaker the blower fan started running, with the thermostat still off. No LEDs flashing since replacing the board.

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Old 09-17-2013, 04:39 PM   #17
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Something keeps running on A/C


You should get a continuos ON led that says power is ON and normal. If the limit was open it would give you that code. Try unplug the wiring harnesses and check the pins in them to make sure none are pushed back or damaged. I suspect you created/got a wiring problem.

Check and remove the G wire from the board. maybe you got a short in it or to it. that will energize the fan. check it where it enters the wiring bundle as the installer may have nicked it and now it is touching R which is hot.
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Last edited by yuri; 09-17-2013 at 05:00 PM.
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Old 09-17-2013, 05:25 PM   #18
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Something keeps running on A/C


Possible thermostat issue?
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Old 09-17-2013, 06:01 PM   #19
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Something keeps running on A/C


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Originally Posted by yuri View Post
You should get a continuos ON led that says power is ON and normal. If the limit was open it would give you that code. Try unplug the wiring harnesses and check the pins in them to make sure none are pushed back or damaged. I suspect you created/got a wiring problem.

Check and remove the G wire from the board. maybe you got a short in it or to it. that will energize the fan. check it where it enters the wiring bundle as the installer may have nicked it and now it is touching R which is hot.
LED is off - no flashing, no steady.
The LED code legend says Continuous On, Control has 24VAC at SEC-1 and SEC-2. Continuous Off, Check for 115VAC at L1 and L2, and 24VAC at SEC-1 and SEC-2.
I unplugged the wiring harness. Pins are perfect.
I removed the G wire. Don't see any nicks on it or the red wire. Blower fan runs with the G wire off.
Only way to stop the blower motor is to shut off the circuit breaker or to keep the safety switch up (fan goes on when I push the switch).
Thanks.
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Old 09-17-2013, 06:03 PM   #20
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Something keeps running on A/C


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Possible thermostat issue?
Thought about that. Seems like it would be a real coincidence that it went out when I had the problem with the filter.
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Old 09-17-2013, 06:17 PM   #21
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Something keeps running on A/C


I was checking the connections at SEC-1 and SEC-2 and followed them up to a transformer. The transformer has a coating of rust. Could that have shorted out? Would it cause the LED not to be on and the blower fan to run? Also, the blower was acting normally and the a/c was working (although the inducer fan kept running) before I replaced the board, so that would seem to indicate that the transformer was working, right?

Last edited by miscrap; 09-17-2013 at 06:21 PM.
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Old 09-17-2013, 06:28 PM   #22
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Something keeps running on A/C


Test for 24V voltage between Sec-1 and Sec-2
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Old 09-17-2013, 06:34 PM   #23
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Something keeps running on A/C


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Test for 24V voltage between Sec-1 and Sec-2
Sorry, I'm new at this. I've got a meter... I have to connect one side to SEC-1 and the other to SEC-2? Do I do this to the plugs coming from the transformer, or the spades on the board? (Sorry, I know this is a stupid question, but I'm afraid of frying the board and having to buy another.)
Thanks for your help.
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Old 09-17-2013, 06:38 PM   #24
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Something keeps running on A/C


you can do it at the board and also check for 24 volts AC from R to C on the board with all the thermostat wires off. Let us know.

Does the new board have a purple 3 amp GM auto fuse on it? Is it blown or missing?

Does the fan run with all the tstat wires off?

The board is programmed for safety to run the fan to "cool off" the heat exchanger if there is a fault.
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Old 09-17-2013, 07:06 PM   #25
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Something keeps running on A/C


If you lost your 24VAC it probably is the source of your problem. On some models of furnaces (Carrier is one of them) the blower will run continuously when the 24VAC power is lost. If you need any help with using your meter just ask.
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Old 09-17-2013, 07:08 PM   #26
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Something keeps running on A/C


Quote:
Originally Posted by yuri View Post
you can do it at the board and also check for 24 volts AC from R to C on the board with all the thermostat wires off. Let us know.

Does the new board have a purple 3 amp GM auto fuse on it? Is it blown or missing?

Does the fan run with all the tstat wires off?

The board is programmed for safety to run the fan to "cool off" the heat exchanger if there is a fault.
No voltage between SEC-1 and SEC-2.
No voltage between R and C with the wires removed at the thermostat.
Purple 3 amp fuse not blown.
Fan runs with thermostat wires disconnected at the thermostat. (as long as I push the safety switch.)
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Old 09-17-2013, 07:08 PM   #27
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Something keeps running on A/C


probably the water shorted the transformer after the board blew. you got no 24 volts to give you any codes so yeah you need a XFMR, transformer. you should get it from Carrier as the mounting of the universals is different so the OEM fits the best.

now I can go back to my CIV 5 and be Alex the Great.
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Last edited by yuri; 09-17-2013 at 07:12 PM.
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Old 09-17-2013, 07:20 PM   #28
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Something keeps running on A/C


Thanks again, Yuri! I don't know what it is you said you're getting back to, but I hope you enjoy it! I'll post the results when I replace it.

One last question... Would that cause the blower to run continuously? And if so, why didn't it do it before I replaced the board?
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Old 09-17-2013, 07:23 PM   #29
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Something keeps running on A/C


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Originally Posted by firedawgsatx View Post
If you lost your 24VAC it probably is the source of your problem. On some models of furnaces (Carrier is one of them) the blower will run continuously when the 24VAC power is lost. If you need any help with using your meter just ask.

Thanks, firedawgsatx! I saw your reply after seeing Yuri's. Your answer about the blower running when 24VAC is lost sounds like the cause of my problem. I'll let you guys know the results when I replace the transformer tomorrow.
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Old 09-17-2013, 07:34 PM   #30
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Something keeps running on A/C


The control board requires 24VAC to open the circuit to the blower motor. If no 24VAC is present it runs continuously like you are experiencing. I am glad you have narrowed down the probable cause. I was thinking you had already verified the 24VAC. As always, that is what happens when you assume.

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