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I have a colman evcon split unit, I had a guy replace the thermostat (old electronic, new mercury) and everthing worked fine. One week later out side unit stopped and was frosted over on the outside. I can push the contactors on the outside unit and got power. I traced wiring down to transformer. I replaced the transformer with one with a circutbraker built in. When i turn the brakers on the transformer curcuit breaker trips...I followed the wiring on the transformer to the best of my ability, help....

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Hi, you do have a dead short in the control side of the system. Good that you bought a transformer with the breaker. Most people don't and will smoke several of them. Anyway, it is a split system. If it was iced up, it must be a heat-pump, not gas fired. The problem will be in either the stat wiring from stat to indoor unit, to outdoor unit, and if a wire is not grounded in the stat wires, one of the 24volt controls have a dead short as the breaker trips instantly. Here is what you will need to do. You will need to do a process of elimination on all of the 24volt controls. I would start at the outdoor unit as you engaged the contactor by finger to check for power. If you see no stat wiring outside touching, the coil on the contactor is 24 volts and may be the shorted control. Coil could be bad. Pull a wire off the coil,there will be 2 wires at the sides. I am sure you know which are the low voltage controls if you can replace a transformer, this is great. You can find this pretty easy. If you pull a wire off one side and reset the unit and the breaker does not trip, then you know the low voltage coil is compromised. If it trips, go to the next low voltage control as the 24 volt coil on the rsv ( reversing valve ) and unplug it. If you have the schematic handy, it will show you all of the componants on the low voltage side/secondary side of unit that you will need to check until the breaker stops tripping. This is the best way to find the culprit!! I have done this for 33 years as a contractor and I am sure you will find this short very soon by doing this. Here is a tip for you also. Sometimes on the transformers that have these tiny resets on them, will wear out pretty fast. What you can do is take a 3 to 5 amp automotive type fuse and on the 24 volt side of the transformer you just cut the red/ hot wire/24v. and crimp a female stak-on to each end of the wire you cut. Then plug each end onto the fuse.Use some electrical tape around it so any bare metal that may be showing will not touch and blow fuse. This is a good way to protect all transformers that have no breaker if you end up with a short. Cheaper to replace a fuse then to keep replacing transformers every time! The fuse will just blow and you can start looking for the short. Now on your unit you can go to the indoor section where the transformer is that you put in. You can eliminate the thermostat and control wiring to the indoor unit and outdoor unit real fast so you know where or which section the short is in. Just kill main power, now where your stat wiring terminates you will disconnect from the control board. Since you have a heat pump you will have more control wires to work with, so either draw a diagram or use the one on your panel to reattach. Remove the wires from the board that take off to the stat first and supply power back to it. If the breaker holds, you will know the short is either the stat wiring from the indoor unit are touching somewhere/grounded or at the stat.You will then know that's where the short is as you have narrowed your search way down. If it trips, you will do the same to the control wires that go to the outdoor unit. If you disconnect it at the board and it holds, you will know it is from the wiring there to the outdoor unit! So, you either have wires grounded from there out or a low voltage control part has burned out. If you remove all of the control/thermostat wires at the board to the indoor and outdoor unit and it still trips, the short will be in the indoor unit which will more then likely be the board itself. Yes sir, this is really a very easy fix for you and I feel you have the ability to do this checks your self. The short has to be on the low voltage side of the transformer as you have proved that! You traced it right back to the transformer secondary low voltage side. So, just take your time and follow my instructions the best you can, and you will find out which part of the system the short is in and then narrow the search down further! I have a hunch the coil is burned/shorted on the contactor :) A place to start by pulling one little wire off the coil. I know this is a long explanation but I wanted you to understand and help you as much as possible on how to tackle this. Sounds difficult but it is not at all. It is either a low volt componant on the outdoor/indoor/ thermostat/ or stat wiring. If none of those, with all low voltage wires removed at board and it still trips, the board is shorted to ground. You can kill power to indoor unit and carefully take the board loose to look at the back side for any hot spots and you will know its the board. I had one totally smoked on a 5 ton package heat pump yesterday in fact!!! I could not see it until I pulled the board/defrost board out far enough to see it, but I knew it was the problem as it would not control the reversing valve, fan control, or run the condenser fan motor. Please drop me a line and let me know how you are doing, please. I would love to know that you were able to find it as I know you will. Best of luck to you.

Posted on May 06, 2010

  • Robert Horton
    Robert Horton May 08, 2010

    Hi there, just checking back to see how its coming along. Please keep me posted.


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