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Discussion Starter #1 (Edited)
I don't have many details right now, but I am hoping to get a general idea.

My daughter's central air unit crapped out a bit ago... It appears there is no power at all..

As you can see by the attached pic, something got real hot and melted the quick disconnect non-fused box...

I have replaced the disconnect box, but still get absolutely no power at the thermostat.. Replaced the thermostat.. Same problem. No power..

Is there a fuse or connector I can test for continuity or voltage??

I repair TVs (Plasmas, LCD, LED, DLPs, etc etc) for a living so I am comfortable (somewhat :vs_worry: heh) around high voltages.. Or, to be more accurate, I know enough (usually) not to fry my arse... :D

Any hints or tips would be greatly appreciated.. I love my daughter and our grandkids immensely, but 2 weeks in the same house.. :vs_mad: heh
 

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Discussion Starter #3
Thanx for the reply.. The inside breakers seem to be OK.. Is there some kind of internal breaker on the unit itself???

Thanx again..
 

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I would check the fuse on the control board. It should be located in the blower compartment in the furnace. Most likely a 3 amp purple fuse.

Sometimes the breaker won't look like it is tripped. I would cycle it on and off a few times.
 

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The disconnect powers the outside compressor. Make sure you have power at your new disconnect.

The thermostat is power by your furnace (Blower), unless it runs on a battery. Check to see if you're getting power at the furnace. Check the breaker for your furnace and make sure the switch at the furnace is on.

Post the make and model of your furnace and compressor.
 

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Discussion Starter #9
Yea... No power whatsoever to the Thermostat w/o batteries in the unit. Brand new Honeywell Thermostat..

Wires are all hooked up right.. BLUE-BLUE GREEN-GREEN YELLOW-YELLOW etc etc

Is there any place on the thermostat or the board (blurry pic attached) that I can check for voltages??

As I said, I can do a new model LED TV blindfolded (and have a 70" Sharp on my wall to prove it!! :D) but I haven't dug into an AC unit before...
 

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First, check to see if you have 240 at the disconnect.
 
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Please get a pro out to determine what melted the disconnect and do the repair.

I know just about the same about electric work as you, possibly a smidgen less, so that puts me in a category of successfully changing a light bulb with real good luck.

A forum, in my opinion, just isn't a very good place for a short course and those are offered sometimes as evening classes for adults if you like.
 

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Put meter leads on teh 2 red wires that go to the 2 inside lugs of the disconnect.

As others, can't say what those black wires go to.
 
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Discussion Starter #17
Want to touch bases and say I appreciate all the replies..

Unfortunately, with my work schedule I won't be able to get back to this until Monday..

I'll definitely touch bases with this thread on Monday and report my results of the checking for the voltages.. I will also get some more internal pics..
 

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Discussion Starter #19 (Edited)
OK I am going to jump back on this today..

Just to clarify, I need to put the probes on the two marked wires and check for AC voltage..

Also check from each of the marked wires to GND, also on AC Voltage...

If I do get 240v, then the problem is on the AC side of the equation. If I don't get 240v, then it's likely a breaker problem at the breaker box..

Sound about right??

I'll also get pics of the other components in the AC itself...
 

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Discussion Starter #20
OK.... Here we go..

Have 248V AC on the two red wires coming out of the house.. Was hoping they would be dead as that would likely be an easy fix.. Breakers..

I get 123v AC on both red wires to GND....

Attached are pics of the other AC Unit components and of the Thermostat wires..
 

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