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    melisawilkey's Avatar
    melisawilkey Posts: 1, Reputation: 1
    New Member
    		  
    #1

    Oct 4, 2012, 02:56 PM
    Central AC unit will not turn on
    I have a Trane xr12 outside and Trane xr80 inside. 2 days ago it was working fine until we upped the degrees on the thermostat so the unit wouldn't continuously run.

    Then it quit working.

    We looked at the 5amp fuse inside and found it was blown. We replaced it.

    At first the fan ran in the on position. Now, I can't get anything to work.

    I have tried testing the thermostat with the R to G method. The fan does not turn on.

    I have checked all breakers and they are fine.

    The 5amp fuse is NOT blown now.

    Any further suggestions?

    I was following a Q/A and following it step for step until the lady was too afraid to go in the attic! So this is where I am stuck...

    PLEASE HELP :) We live in Florida and it is still in the 90s here. Thanks...
    drtom4444's Avatar
    drtom4444 Posts: 3,282, Reputation: 145
    Ultra Member
    		  
    #2

    Oct 5, 2012, 06:50 AM
    Yes, check to see if you have control voltage of 24-30 volts. If not, you burned out a transformer. This is usually caused by a shorted main contactor in the outside unit. It is the main relay that works on a coil that pulls it in. With your ohm meter check the ohms on the coil, which should be from 500-3000 ohms, if lower change it. Get one that will handle higher amps, so if you have one that is a 20 amp contactor go to a 30 or 40 amp one, etc. You will also have to change the transformer. Get one that is much larger with a pop-out circuit breaker on it. Also, check the other connections and wiring because sometimes you can have wires shorted out from a rat chewing on the t-stat wires which can melt them all together. In that case you will have to run new wires or find some good ones in the bundle, but changing the whole wire is best. You always disconnect the wires from a coil before checking it, and you check the wires going to the coil to see if they are shorted.
    Here are some wiring diagrams: https://dl.dropbox.com/u/8010163/AC%...20Diagrams.zip
    Almost all AC units are wired the same.
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