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Manage My Life

Damaged wire from Thermostat now AC won't run.

by Manage My Life Last activity date:
August 23rd, 2011

The Thermostat cable got damaged when I was out of town, and I don't know how. When I came back I saw two ends of cable one coming from the house and one from the outside unit. I assumed that the wires were just straight through and connected them back together. After connecting them I wrapped all of the connections in Rubber galvanizing tape and then electrical tape to keep moisture out. Unfortunately at this point I didn't check to see if the AC would turn On. It didn't when I eventually checked, is there a breaker/fuse that is installed from the Thermostat wires into the unit? I have a Trane Model #4TWX4042B1000AA.

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Building Supplies
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Answers (7)
Lyle W
That transformer should be in the electronics for the air handler inside the house. If that air handler is in your attic, you will probably find the transformer in the control box for that component.
by Lyle W
August 23rd, 2011
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Manage My Life
I didn't have 24V on either of the two sets of wires. I am attaching the schematic that you sent me with a question. Where is the transformer at? I have highlighted the yellow part of the schematic that I am looking for. Is this component or wiring in the unit in my attic? I am including a picture of what is in the outside unit.
by Manage My Life
August 22nd, 2011
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Manage My Life
Thanks for the response, I guess that R-B and Y-B being colors made sense. I just wanted to be 100% certain. I feel confident that I can check the voltage safely. Will let you know what I find.

Thanks
by Manage My Life
August 22nd, 2011
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Lyle W
On that defrost control board, the troubleshooting that you are describing indicates that you need to check for 24 volts between the Red and Black wires (marked on the wiring diagram below). You will also need to check for 24 volts between Yellow and Black (also marked). If the control board is getting power and the LED light is not on, then you probably have a bad control board. If you are not getting power, then you could have a bad power supply or a wiring failure. I do not recommend that you conduct that live voltage check unless you are completely confident in your technical ability so safely measure it using a volt/ohm meter. Disconnect electrical power as soon as the voltage check is completed. The other troubleshooting step involves using an INSULATED jumper wire to short across the connection marked DFC_DFT on the control board to a pin marked TEST_COMMON. I don't recommend that you conduct that test yourself. A service technician will need to perform that check. These additional tips may help. If you need more assistance, reply with additional details.
by Lyle W
August 22nd, 2011
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Manage My Life
I just checked my wiring again to make certain there was no loose connection. I went from the front of the splice to the wire nuts and I had continuity. So this is the problem, when I removed the upper cover where the coil and the large capacitor is mounted I noticed that there was a control board that has a Green LED mounted on it. The LED was OFF, I am attaching the numbers that I took off of the Control Board.
21C140501G38 and CNT04364 Scroll.

I found the Demand Defrost Controls Checkout sheet in the unit.
1. LED Off - Check the following 1. 24V R-B at board and 24V Y-B at Board 2. Short FRC_DFT pin to TEST_COMMON pin.

Could this be the issue that it isn't getting the control voltage? I don't understand the terminology R-B and Y-B?
by Manage My Life
August 21st, 2011
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Lyle W
I do not see a fuse in the typical thermostat installation for this unit. I provided a wiring schematic for this system in the image below. That information may help you check the wiring and determine the cause of your failure. You may need to have a service technician physically examine the system and help you with repair. Here is a link for the Sears Service website:

Sears Home Services

.

If you need more help, reply with additional details and we will try to assist you further.
by Lyle W
August 19th, 2011
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Manage My Life
I understand how frustrating it can be with the air conditioner not working. I have taken the time to research on the Manage My Life website and have located a link that you may find useful. While you are waiting for a detailed reply from an expert i have attached the link below
Answered in 24 minutes
by Manage My Life
August 17th, 2011
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