Air Conditioning Unit Not Working, What Could Be Wrong?

I purchased a house in December so naturally I did not try the air conditioning unit outside unitl the last couple of days. I do not have a heat pump just a Trane XE 1000 air unit. The thermastat is one that you have to program and I have not been able to do that very well. I noticed the house not cooling down but yet I could hear the furnace running so stupid me thought everything was ok until I noticed that the unit outside was not running. I checked the breakers on the inside of the house and also the breaker outside near the unit but nothing so far is working. Could it be something about not programing the thermastat correctly or is it more likely something wrong with the air conditioner?

  1. Comment by francis g
    February 28, 2010 @ 4:00 pm

    if you turn your thermostat to turn on cooling, listen for the click of the contactor. you ll also hear a hum. if you do hear it humm, your stat is fine. next, i myself would look at the capacitor. it holds a charge to jump-start the compressor. often they go bad or get weak. they sell “hard-start” kits, but personally wouldnt recommend doing it yourself unless you know how to short out the capacitor bc it ll shock you bad. finally if its the compressor, you re better off getting a new unit. look at the date code on the unit, it may be under warranty, at least the parts, not the labor. after all, we gotsa eat

  2. Comment by green_wa
    February 28, 2010 @ 7:33 pm

    Both answers above are reasons that i may not work, but one other thing i would suggest is replacing the thermostat with a non-digital one. I work at an apartment community and there are digital thermostats in each unit. As a problem occurs with a unit we fix it and replace the thermostat. A lot of people do not use them correctly and if something does go wrong with it, it is hard to diagnoss. I have had plenty of AC units that were doing what yours is and all that needed to happen was replacing the thermostat because of internal failures. Between this and the above mentioned fixes, it should solve your problem. You can get a standard thermostat for under $30.
    Also, just because your low pressure swich trips doesnt mean you are necessarilly low on refrigerant. There should be a little button on the outside of the outdoor unit near where the refrigerant lines come in. push this and it may alleviate your problem. Check also to make sure the 24v is going to your contactor (should be a yellow wire). If it is not your thermostat is most likely the problem.
    Let me know how it turns out :)

  3. Comment by Derek
    February 28, 2010 @ 10:31 pm

    One other thing to check and is much cheaper. There should be a disconnect out by the ac unit. Sometimes the fuses in these pop. If one of them is bad its a simple fix just go to the Home Depot or Lowes and get one that is the same rating and replace it. If you do not like messing around with electricity then I would call an HVAC tech to come look at it. Just remember that even if you cut the power at the disconnect one side of it is still hot. You must flip the breaker at the box in your garage before its totally dead.

  4. Comment by Thunderh
    March 1, 2010 @ 2:13 am

    The problem could be many as mentioned such as no 24 volts to the contactor, not calling for cool because the t-stat is not set right. My suggestion is to go to the following site and the info will be helpful. One way to check the outside unit to determine if you have 24 volts is to depress the switch on the contactor and see if the unit comes on. If it does then most likely the low pressure switch cut out. If nothing happens and you have a meter check to see if 240 volts is going to the contactor. Depress the switch and see if it comes out the other side. If you have power and the unit isn’t coming on I would look at the capacitor to see if its domed. I don’t recommend a novice change this because these can hold a 370/440 volt charge which can cause death or injury. The below listed web site will show some diagrams of the items discussed as well as list most likely and least likely causes.

  5. Comment by Eamonn S
    March 1, 2010 @ 6:54 am

    If the furnace runs in cooling mode, and the outside unit does not, there are two things to look for;
    1 the contactor is not working at the condenser, this is a low voltage device that uses 24v to close a magnetic switch that connects 220v to the condenser.
    2 the condenser has a low pressure switch which will not allow it to run if you are low on refrigerant, ergo you have a leak. If it’s #2 use a contractor as accidental discharge of refrigerant into the atmosphere is illegal.
    Hope this is helpful.

  6. Comment by robert
    September 22, 2010 @ 4:32 am

    it freeis up all the time

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