3a fuse keeps blowing

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  #1  
Old 03-02-16, 01:27 PM
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3a fuse keeps blowing

I have a Carrier 58pav110 air handler system and a carrier condensor outside as well as a honeywell digital thermostat...well problem goes that my thermostat wouldn't come on so I started to troubleshoot the system, at first thought it was a simple 3a fuse, system turned back on for a few then shut off once system kicked in and fuse blown again...so I decided to try a new transformer today...well the system won't even turn on now and the fuse would blow immediately...so next I tried a new conductor coil (relay) on the condensor...same thing system just blows the fuse right away. error code on motherboard states fuse in blown (obviously)...I checked all the wiring, nothing pinched nothing touching and everything still seems good...the transformer may have blown though, a quick ohm check on secondary side didn't yield good results so i'm off to get another transformer but i have a feeling that isn't the only problem...this time I'm going to fuse the transformer on the secondary side with a 3amp fuse and then cross my fingers at least the system turns back on...is there anything else i should check for?

o i also disconnected all the wires from the thermostat on my board to eliminate a short coming from the tstat side and the system still pops the fuse
 
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Old 03-02-16, 01:37 PM
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.I checked all the wiring, nothing pinched nothing touching and everything still seems good...
It would appear something is touching ground.
Go you have a test meter ? Check from each stat wire to ground.

You have ALL the control(stat/condensor) wires off the control board and it stills blows a fuse ?

You don't have a heat pump so unless you are using the A/C.... changing the contactor wouldn't be the problem.
 
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Old 03-02-16, 01:49 PM
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I had all 5 low voltage wires disconnected the white red yellow common (black) and green off the board and not touching anywhere and the fuse still blew...i disconnected the secondary wires from the transformer and it didn't blow but figured no power at all wouldn't make it blow
 
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Old 03-02-16, 02:31 PM
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The output of the 24 VAC transformer goes to Sec1 and Sec2. Disconnect those wires and see if you are still getting a short. You should NOT be getting a short under those conditions.

I would suspect a short on the circuit board itself.With the transformer disconnected as described above, I'd do a continuity test between the g terminal and sec1 and sec2. Both tests should show no continuity. If there is continuity, you likely have a short on the circuit board you should investigate.
 
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Old 03-02-16, 02:56 PM
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The circuit board is less than a year old...only thing I can think of is the connector that plugs the wires into the board is kinda old and dirty and looks bad but I wouldn't know how to replace the connector (not the wires but like a big plastic connector that plugs into the board)
 
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Old 03-02-16, 05:25 PM
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The big plastic plug could be dirty but that wouldn't cause a short.
Try powering up the board with the 11 pin PL-1 disconnected.

I'm looking at an old schematic for your furnace. The 24vac should take two paths. One path is not fused and goes directly to the electronics on the board. That's how the board knows the fuse is bad. The other path is fused and goes thru safety stats via PL-1 and then ends up at R.
 

Last edited by PJmax; 03-02-16 at 05:45 PM.
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Old 03-02-16, 09:33 PM
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11pin PL1 would be the big connector?

I also tested with sec1 and sec2 disconnected, no short (fuse stays good)
I haven't done the continuity test yet, my cheap multi meter doesn't have that function and I can't find my continuity tester at the moment but will do so sometime after work tomorrow.

My guess is, if I can get the system to turn on again like before, I think my blower motor is bad causing the fuse to blow...but at the moment I have to get it back to that point before I can diagnose that particular problem, I'm hoping swapping in a new transformer in the AM (with a fuse on one of the SEC wires to protect the transformer from blowing again) will do the trick
 
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Old 03-02-16, 11:16 PM
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The fuse is ONLY there to protect the 24v wiring. The blower has nothing to do with it blowing.

Of course the fuse won't blow if the transformer is not connected. You could also use 2A fuse for testing.

There are several variations of boards that are used in that line of furnace based on age. From what I can see.... the 24v fuse only protects the wiring....not the board. You need to get 24vac back into the board. You need to see if the fuse doesn't blow if the only 11 pin plug on that board is unplugged.

You said the fuse blew with all the thermostat wiring disconnected. That's telling me you have a short to ground in the safety stat lines. That would be the round two prong devices fastened to the metal plenum. When you unplug the 11 pin plug.... these safeties are disconnected from the board.
 
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