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Old 04-22-2012, 03:23 PM   #1
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a/c fuses?


I was replacing a thermostat to my central heating/a/c. while re-wiring the new unit, there was a pop and now there is no power. The Honeywell guy told me that I probably blew a fuse. However, I can't find any fuses anywhere. Can somebody please help me with this? We don't have the funds to hire a professional for something that sounds so small. It's over 100 degrees today and I have kids in the home. Thanks a bunch!

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Old 04-22-2012, 03:26 PM   #2
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a/c fuses?


May have to open up your unit and see if there is a fuse on the circuit board.

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Old 04-22-2012, 03:47 PM   #3
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a/c fuses?


Many times you will find it in the inside interior air handler. It is usually a 2 or 3 amp car fuse. Sometimes there is already a spare in there.

Turn off breaker(s) before removing panels.
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Old 04-22-2012, 03:51 PM   #4
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a/c fuses?


To add a little to what Darren posted..
Your thermostat needs 24 volts AC, but depending on the furnace design, the 24 volts could be from the control board in the furnace or you may have a small transformer mounted somewhere that is providing the 24 volts using house power.
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Old 04-22-2012, 04:23 PM   #5
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a/c fuses?


i appreciate the answers. However, I have taken off the panel to the a/c unit, and there is a main board (like in a computer) but no fuses, and no indication that anything was wrong. Also, there is a box on the house by the a/c unit that I opened and it actually speaks of fuses on one part, but then the panel below says there are no fuses contained. Because of the popping and the way the whole thing happened, a fuse sounds like the most logical answer, but the problem is that I still can't find any fuses. Also, I have read that there may be a restart button on the unit as well, but could not find one of those either. Any more suggestions?
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Old 04-22-2012, 04:31 PM   #6
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a/c fuses?


Where did you hear the pop? Near the thermostat or from outside?
Look on the furnace panels/backside of a door for a wiring diagram and look for a fuse. Usually indicated by a ~ kind of symbol.
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Old 04-22-2012, 04:32 PM   #7
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What is the brand name of the unit?
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Old 04-22-2012, 04:34 PM   #8
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You sure it wasn't the circuit breaker? A lot of times it is hard to tell they are tripped. They must be switched to off position and then back to on.

There should be a fuse on that circuit board, but they don't make noise when blown.

Try the breaker.
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Old 04-22-2012, 04:35 PM   #9
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Did you check the breaker. If the breaker is still on maybe turn it off and turn it back on and see if it resets itself.
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Old 04-22-2012, 05:20 PM   #10
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Thanks, but yes I've tried the breaker. And, no it doesn't need to be replaced, because I switched the one from the upstairs unit and still the same results! I'm at a loss. there is like a "motherboard" under the panel on the a/c unit, but nothing that looks wrong or blown.
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Old 04-22-2012, 05:35 PM   #11
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Post a picture or two. Make and model number of the furnace would be nice as well.

You need to check for 24 volts across the R and the C terminal on the control board.

With the furnace door off and the door switch held in, is there an led light on the control board that is lit up? If not then the board is not receiving power. This is going to be a fuse or the transformer.
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Old 04-22-2012, 05:35 PM   #12
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The unit is a Puron by Carrier. The popping and spark came from the wires coming from the wall intended for the thermostat. I was connecting the wires to the thermostat at the time. Model 38EYG048300.

Last edited by twenta; 04-22-2012 at 05:38 PM. Reason: added model number
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Old 04-22-2012, 05:36 PM   #13
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Quote:
Originally Posted by jammin06 View Post
There should be a fuse on that circuit board, but they don't make noise when blown.
They certainly do.
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Old 04-22-2012, 05:39 PM   #14
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Quote:
Originally Posted by twenta View Post
The unit is a Puron by Carrier. The popping and spark came from the wires coming from the wall intended for the thermostat. I was connecting the wires to the thermostat at the time.

No, the unit is not a Puron by carrier. Puron is the type of refrigerant, hfc 410-A to be exact, first used by Carrier and that correlates to the condensing unit, not the furnace.

Model numbers would help.

Yes, you needed to turn the breaker OFF to the FURNACE prior to any stat work. You blew the fuse or the transformer as it was live.
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Old 04-22-2012, 06:05 PM   #15
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Quote:
Originally Posted by Code05 View Post
Many times you will find it in the inside interior air handler. It is usually a 2 or 3 amp car fuse. Sometimes there is already a spare in there.

Turn off breaker(s) before removing panels.


Being a Carrier unit I believe Code 5 is right on. Look for an automotive 3amp or so plug in type fuse on the control board that will be located in the air handler inside of the house.. They do not "pop" and make a noise so much.


Last edited by Jeeps; 04-22-2012 at 06:19 PM.
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