3 Amp Fuse Keeps Blowing On Control Board


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Old 04-10-13, 05:23 PM
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3 Amp Fuse Keeps Blowing On Control Board

The 3 amp fuse keeps blowing on the control board when the AC kicks on. It does not happen when the heat cuts on. It appears that the problem is with the outside unit. I have done a lot of troubleshooting and determined it is not the thermostat or the wiring that goes to the thermostat. The system will work when I disconnect the 24v wiring that is connected to the outside unit. The AC cuts on and blows air and does not blow the fuse.
I checked all visible wiring. The wire was actually cut where it runs out of the attic unit. I fixed this by cutting off the bad portion and then restripping the wires. This did not fix my problem.
I just purchased this house a couple of months ago. It was a foreclosure and had nobody in it for a couple of years. Therefore the AC hasn't been used in a while.
The capacitor in the outdoor unit seems to still hold a charge. I know this because, well, it shocked me.

Any ideas as to what the problem can be from here?
 
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Old 04-10-13, 05:49 PM
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Welcome to the forum.

Shocked I'm shocked

Those caps don't usually hold a charge for that long.

Apparently you have a problem in the outside wiring. If I were working on that I would disconnect the two wires at the inside air handler that go to the outdoor compressor. Check between one wire at a time and ground. You should see no resistance or meter movement. If you see any resistance or meter movement when checking to ground then you have a wiring short.

If you see no resistance to ground..... go out to air handler. Shut off power to compressor. Remove the two small wires from the contactor coil. Go inside and try the air. The compressor won't run but is the short gone. If all ok..... the contacor coil is shorted.

Let me know if this is a heat pump because there will be additional wiring to outside unit. If there are only two wires to outside unit then it should be a standard AC system.
 
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Old 04-11-13, 05:40 PM
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Thank you so much for your help! It turns out it was the contactor coil. Unfortunately, I lost my patience a little too soon and ended up paying a guy $300 to fix it. (I sat down at my computer desk and was greeted by hundreds of ants so I said "screw it" and I called the guy.)
I told the guy that it was the coil when he got here and then explained to him what I had done. He told me that I saved him a bunch of time but he still had to charge me. Oh well.

I want to thank you for actually helping me with my problem! I posted this exact same post on another forum, and their answer was to repeat exactly what I told them in my post that I had already done.
Also, thank you for explaining to me how to check for a short. I knew it could be done with a multimeter, I just didn't know how to do it.
Hopefully I won't have any more AC problems, but if I do, I know where to come!
 
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Old 04-11-13, 05:46 PM
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I guess your next post will be in the insect control forum

At least the problem is fixed. You learned how to diagnose wiring and that can be a real help in problem solving........ that and a multimeter
 
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Old 05-03-13, 01:13 PM
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Sorry to interrupt, I ended up finding this as I have the same type of situation with my goodman A/C...

Blows the 3 amp fuse on the electric board on my furnase, but the AC does start when the spring is depressed on the contactor. Wires seems fine...

if I understand correctly, in this case, it was the contactor's coil... So I'm assuming that you just switched the contactor for a new one?

Thanks in advance!
Morrow_d
 
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Old 05-04-13, 11:38 AM
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Welcome to the forums.

Right......the actual coil was shorted.

If you disconnect the two small coil wires to the contactor and the 3A control fuse no longer blows......then you have found your problem. Replace the entire contactor.
 
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Old 05-06-13, 05:37 AM
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Thanks!
I will change this as soon as I get the new one, as it does look like to be the coil.
 
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Old 07-05-13, 03:10 PM
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Great help

You guys saved me time and money. My furnace was blowing the 3amp fuse and my AC wasn't coming on. When I manually pressed on the conductors plunger on the AC unit it worked but wouldn't come on automatically. I replaced the conductor ($18) and everything works perfectly now. Thanks!
 
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Old 07-13-13, 09:48 PM
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Where do you guys buy the contactor? I was having the same problem with the blown fuse and it sounds like it's the contactor but there is only one web site that is selling my contactor model.
 
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Old 07-14-13, 07:56 PM
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It can also be the wire between the house and the compressor unit. Very easily damaged by animals, the weedwacker, etc.

You should follow the directions above and heed the warning in red to determine if it is actually the contactor at fault.

You can get the contactor from a local HVAC parts house or online. A few online links below.

North America Hvac Parts
HVAC Parts Outlet
 
  #11  
Old 10-15-13, 06:27 PM
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Thank you so much for this thread! It's been reallly helpful!

I followed the steps described here and found that I have a shorted contactor. I removed the contactor:
45DG10AJA758R by SIEMENS - Buy or Repair at PLCCenter - PLCCenter.com

I took it to my local Grainger supply and the original is not available anymore. They gave me this one as a replacement:
SQUARE D DP Compact Contactor, 277VAC, 25A, Open, 2P - Definite Purpose Magnetic Contactors - 4DC98|8910DP22V04 - Grainger Industrial Supply

I installed it, confirmed exact same wire-up as what I removed, confirmed 240v supply, confirmed 28v from the control board, but still the outside unit would not start up. I suspect it is because the capacitor is not charging because the new contactor is a double spring type and the original was a single spring on one pole? The capacitor does not show any visible signs of being bad although it does look like it was replaced at some point.

Any suggestions are greatly appreciated!
Thanks in advance.
 
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Old 10-15-13, 07:57 PM
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We had some posting issues with imhi2002. I had responded to him in a PM while we worked on the issues.

It turns out that Grainger sold him a two pole 30a contactor with a 277vac coil.
 
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Old 10-17-13, 05:06 PM
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yep, got the right contactor today and it's working great! Thanks for your help!
 
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Old 10-17-13, 05:54 PM
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Thanks for hanging in there and for the update
 
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Old 02-06-14, 04:43 PM
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Hi there,
I just bought a brand new contactor and the problem with the fuse still happens. I checked the wire and the needle does move when I connect them to ground and check upstairs in the blower end of the wire. But I am confused, If there is no movement on the meter that means there in an extremely large resistance thus a short, not the other way around. So I checked the inside and outside wire and they all give me a ohm reading, just like when you put the two ends of the multimeter together.

What else could be the problem.

Thank you...
 
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Old 02-06-14, 05:37 PM
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Fede I recommend purchasing a digital meter if you want to find a short.
 
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Old 02-06-14, 06:03 PM
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HI there Houston, I just checked with a digital one and everything seems to go as he explained in the instructions for the wires. They are fine, but I still have the problem...
 
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Old 02-06-14, 06:16 PM
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If you think there is a short..... disconnect the wires from the compressor unit and at the air handler. If you check to ground and they show continuity..... a reading..... then the wires need to be replaced.
 
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Old 02-06-14, 08:10 PM
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Hi PJmax, thank you for the response. I disconnected the wires from the blower side and the outside unit and connected the outside part of the wires to ground then checked each wire on the handler side against the ground and they all gave me an ohm reading. Im guessing this means there is a short?

Thanks again...
 
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Old 02-06-14, 08:15 PM
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Do not connect any wire to ground. You want to isolate them.

Unwire the low voltage connections to the outdoor unit and indoor unit and measure for resistance between your wires and then measure for resistance to the copper refrigerant piping and ground.
 
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Old 02-06-14, 08:21 PM
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I sometimes just unwire and isolate the control wires at the outdoor unit and replace the 3 amp fuse then give the stat a cooling demand. If the fuse doesn't pop, I check for a short in the outdoor unit.

 
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Old 02-07-14, 07:12 AM
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Cool I'll try the cooling without the wires to the outside unit. What if it pops the fuse, it couldn't be the high voltage right?. Should I do something about the inside wiring as well?
 
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Old 02-07-14, 07:35 AM
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So I just did that and the fuse popped again. This means the inside wire is shorted?
Thanks...
 
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Old 02-07-14, 10:00 AM
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It only means that the short is not in the outdoor unit.
 
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Old 02-07-14, 12:13 PM
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Ok, so far I checked the inside and outise wires and they are both good. So I went ahead and put a new fuse and disconected all the external wires to rule out shorts in the wires. I jumped the system by conecting the XFMR-R(red wire in the thermostat panel) and the 0 wire on the t92s7a22-24 inside the air handler relay wire (white wire on the thermostat panel) and this blows the fuse. So my idea is that either the relay or the transformer are shorted. Thoughts?
 
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Old 02-07-14, 04:40 PM
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I could offer better assistance if I knew what you are looking at.
Post the make and model number of the air handler.

A picture or 2 wouldn't hurt either...
Photo and image hosting, free photo galleries, photo editing
 
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Old 02-08-14, 08:07 AM
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Hey guys it can be frustrating to find a short in the low voltage system. I have seen the actual thermostat wiring itself be bad and had to pull the entire run and replace it. If you look at the wiring it has up to 8 tiny little wires with really thin insulation and if it stretched and pulled a little too much when trying to get into position on a install I think it can cause the wires to internally short underneath the sheathing. Other more common culprits are the coils that activate sequencers/contactors/relays and of course chew happy mice and the neighbors new chew happy puppy at the outside unit and your teenagers attitude when weed wacking LOL. With a good meter this is very doable though, just have to figure out how valuable your time is. Plus it is fun to DIY sometimes typically when you are trying to avoid a chore that you do not. Sigh it is time to get all my tax crap together I wonder how long that I can procrastinate and act like I am busy really helping people fix their hvac units. Hey do not laugh this is important work here.................................. ask me something anything and hurry up before my wife comes in here and asks how the tax prep is going..........
 
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Old 02-08-14, 09:26 AM
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Looks like Fede has removed all field installed control wires from the air handler and the fuse still pops.

Its probably a shorted wire in the unit but It is hard to say more without knowing what we are working on.
 
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Old 02-08-14, 04:19 PM
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Hi, again thank you for the help. It ended up being the fan relay that was shorted it even had a burn mark in the back. So i went ahead and bought an new one and the one I got is stuck, but it is now too late to go exchange it. I have to wait until Monday now...

But it's all good after checking every single wire and component to see what was the issue I learned a whole bunch about fixing an AC unit.
 
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Old 08-28-14, 08:24 AM
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Hey, found this thread and have exhausted my troublshooting ability...I need some direction.

I'm having the same fuse blow...I have determined that I don't have any shorts in the house wiring (via multimeter), the contactor seems to be working without shorts (16.5ohms on the coil and no shorts). Fan will turn on via jumper (G & R) or via switch on thermostat.

Any attempt to use thermostat will pop the fuse.
once I jumper yellow or orange the fuse pops.

I am thinking maybe the reversing board (not sure what it is called)... help!
 
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Old 01-25-15, 12:30 PM
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This has been a very helpful and informative thread that has attracted a lot of attention.

If you have the same problem and cannot resolve it based on the help listed here.... feel free to start a new thread.
 
 

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