AC Unit will not turn on


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Old 08-06-13, 02:01 PM
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AC Unit will not turn on

I went away for a month and a half and the AC unit broke down while I was gone. One of my dogs had chewed on some wires which I believe caused the problem. The the pipe shown in the pictures was dripping water or something. I can't tell you whether it was from condensation or an actual leak, but my wife thought it was condensation so she wrapped the pipe up tightly in with some padding, and I think water built around the open wires and shorted them out.

Here is the damage to the wires:

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The wire leads into the AC unit at the bottom right and a yellow and blue wire split from it. (below) I am not sure what they lead to. The label is not legible anymore. I have a company coming to fix it, but I'd like to fix these wires first to prevent them from having to come out.

I think these wires are coming from the thermostat and carry the signal to turn on. How do I secure power from these wires? Will they shock me if I touch them?

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Also, what would be leaking out of these pipes? Is it common for water (or something else) to be dripping from them? If I am not being specific enough just let me know. Do they need to be covered up again with foam padding?

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Here is another picture of the wires

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Big thanks in advance for any advice here. Relatively new homeowner here so there is lots to learn.
 
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Old 08-06-13, 02:32 PM
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The yellow & blue wires inside the unit appear to be the low voltage (24VAC) wires connected to the contactor coil. The contactor is a relay that sends 240VAC to the compressor unit when the thermostat calls for cooling. When the thermostat is off or not calling for cooling, there is no voltage across the yel/blue wires and the contactor is "open". When the thermostat calls for cooling, it sends 24VAC to the yel/blue wires which energizes the contactor (closes the contacts), sending 240VAC to the compressor. 240VAC from the house comes in through the heavy red & black wires coming out of the plastic pipe and attached to the bottom terminals of the contactor. The black & red wires coming off the top terminals of the contactor go to the compressor and condenser fan (in conjunction with the capacitor).

In the third picture, showing the gray plastic pipe and the two copper lines (one thin, other thick), the copper lines run into the house to the evaporator coil which gets cold and is what cools the house (with airflow through the evaporator). The thick pipe should be cold and the thin pipe should be warm/hot (if everything is working correctly).

You mentioned water coming out of the pipe in the first picture. I don't see any pipe, only wires with the outer jacket (insulation) removed. There shouldn't be any water dripping from anything outdoors with the possible exception of a small amount of condensate dripping from the thick copper pipe (normally there is insulation wrapped around the thick pipe).
 
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Old 08-06-13, 03:37 PM
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Thanks Bob for that solid explanation. I didn't explain the leak/condensation part very well. It was coming from the large copper pipe, so no problem there.

Now knowing that the wires are de-energized (in absence of a multimeter), I stripped them back and the copper looks darkened, almost dark gray but still slightly brown, but it's definitely not the color of a shiny new penny.

Am I going to need to run a new wire to the AC unit from the thermostat? I cut the wires back and reconnected them, but still no sign of life when I turn the thermostat on.
 
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Old 08-06-13, 03:52 PM
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If the wires shorted together, hopefully all you did was to blow a fuse. The 24VAC is provided by a small transformer, usually located inside near the furnace or air handler (blower). Many systems have a 3 or 5 amp fuse in series with the wire going out the the outdoor unit so that if something bad happens (wires short, contactor coil shorts, etc.) the fuse will blow rather than burning out the transformer. If the insulation on the individual wires is torn so that the wires can short together, that section of the wire should be replaced, or better yet, replace the entire length of wire.

So, replace the wire and check for a blown fuse or transformer.
 
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Old 08-06-13, 04:39 PM
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I am having a difficult time locating the fuse or transformer. I removed the front cover of the contactor coil to check for something and I found something in there with 2 contacts on each side and they looked like they were in really bad shape. It's kind of hanging loose in there now. I may have messed up because a little spring or coil thing popped out into the dirt and I can't find it. I don't know the importance of it, but I suspect it's a pretty important little spring.

Here are some pictures of it below. The last picture shows there is a fuse somewhere. I'm currently trying to research any manuals that might hint where it is.

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Old 08-06-13, 04:47 PM
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The first couple of pictures in your latest post show the contactor. That's likely where the spring came from. I agree, the contacts do look in pretty bad shape. I would strongly suggest that you buy a new contactor. They're relatively inexpensive and are easily replaced by the average homeowner. You need to determine what the specs are on the contactor (single pole/double pole and amperage). Be sure to turn off the power to the outside unit before doing any work on it. Once you have the replacement contactor, take pictures of how the current contactor is wired and draw yourself a little schematic as well. You should get a schematic of the new contactor, as the terminals may or may not be in the same location as the old one (unless it's an exact replacement).

The transformer and fuse will be inside your house, located somewhere near the furnace (if you have one) or the air handler (if you don't). Note that not all systems have a fuse, however many do.
 
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Old 08-06-13, 04:48 PM
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My AC unit is outside and the furnace is in the attic. Were you talking about a fuse located on the furnace inside?

Edit: after further familiarizing myself with how this system works and re reading your post, you obviously were talking about a fuse inside the furnace.

I found a fuse that's not blown on the circuit board in the furnace. It's 32v but says nothing about amperage. That sounds like the fuse you're talking about though, correct?

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Last edited by pandee; 08-06-13 at 06:04 PM.
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Old 08-06-13, 06:45 PM
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You must replace the contactor before proceeding any further.
 
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Old 08-07-13, 04:10 AM
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As Kevin mentioned, you need to start by replacing the contactor. The fuse you found inside the furnace comparment is very likely the fuse I was referring to. If the fuse is good, you may have burned out the transformer. It will be a small box 2-3 inches wide with 4 wires coming out of it, often two on each side. Line voltage (usually 120VAC) goes in on one side and 24VAC comes out. The 24V feeds the thermostat, which in turn feeds the line running to the outside unit (and the air handler). If your thermostat plugs into a mounting plate, remove it and (if you have a voltmeter), check for voltage between terminals RC and C. You should have ~24VAC. If you don't, then the transformer is likely burned out.
 
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Old 08-07-13, 04:13 AM
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some thermostats don't have a C terminal so you should check voltage instead at the control board.
 
 

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