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  1. #1

    what are the top 5 things to fail on AC's and Furnaces

    I just wanted to find out the common things that break on a service call. So I can pay some extra attention to them while I'm in classes. In the beginning classes everything is running and we mainly do the activity that is in the lab manual. Like checking our superheat and sub cooling under different loads, charging/recovery/evacuating or wiring the compressor. My best guess is that anything that is moving like the compressor, contactors, fan motor. I'm also thinking that some parts are really expensive to replace. The reason I'm asking is that these next 3 days we have a open lab before class ends and I just wanted to get familiar with what I am mostly likely to find out in the field.

  2. #2
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,440
    Not trying to be a jerk, but I find myself good at it, so I'll stick with it.

    Rather than trying to pay attention to the 'common' failures, you'd do well to pay attention to the basic theory of heat transfer.

    Learn about airflow.

    Learn about pychrometrics.

    Learn about electrical circuits.

    You'll figure out what commonly fails soon enough.



    Last edited by jpsmith1cm; 06-24-2011 at 05:28 PM. Reason: typo

  3. #3
    Join Date
    Jun 2011
    Location
    Central Indiana
    Posts
    613
    jpsmith is right, dont study for failures, study for how things are supposed to be. There are some failures that are more common but studying to find them isnt the way to get a good education. If you want to be a good service tech, learn everything equally so you can handle everything equally.

    Now I will sort of answer your question. The most common problems I find when working on the cooling side of the business are, incorrect charge (over charge or under charge) and other refrigeration cycle problems (obstructions, bad txv's and the like). If you understand the refrigeration cycle inside and out (literally) and the symptoms to each problem, you will be fine Also electrical issues, whether its a electrical component failure or an electrical issue that caused a component failure, you have to know electrical circuitry theory. The other big one is air flow.

    If you study all areas you will be prepared. Yes there are certain things that are more common than others but every single system is different so you will never know what your getting into. Everything in a system can fail.

    I respect that you want to be as prepared for the field as you can be, but nothing will really prepare you for the field better than being there. So just work hard on the basics and be prepared for the next half of your training, the in-the-field work.
    The only true knowledge is the pursuit of knowledge

  4. #4
    Join Date
    Jun 2005
    Location
    Winston-Salem NC
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    1,133
    Learn the order of operation for the various systems.
    If you know what is supposed to be doing this at that time, then it isn't difficult to figure out the problem.

  5. #5
    You guys are right, my question probably shows my greeness. I guess a better question would be what should I do during a open lab. The teacher is in and out of it and there is all this equipment and everybody just ends up leaving early. I paid for the time in the lab and I'm just trying to think up of activity to do. Like if you don't go in with something to do then nothing will get done. Like if I had a bunch of things to investigate, I can open the covers on a couple of units and at least try to think how I might go about replacing these specific parts. The labs we are getting a have us covering the condensors with card board to see how that affects our superheat or the amperage draw on the compressor. We can practice charging/recovery. I'm just trying to do something out of the box, that won't blow up in my face. Isn't it everybodys dream to get open lab any ideas? I'm looking for inspiration, I won't do anything that I can't justify.

  6. #6
    Join Date
    Sep 2008
    Location
    Western PA
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  7. #7
    Join Date
    Jun 2005
    Location
    Winston-Salem NC
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    1,133
    Do you have parts to replace broken parts with?
    Learning what a burnt transformer smells like is good knowledge.

  8. #8
    Join Date
    Feb 2010
    Location
    Ontario Canada
    Posts
    1,339
    Do not know where you live, but if you live in an area where heating and cooling are relatively equal, I would spend a bit of time trying to find a crack in a heat exchanger. I do not know if your lab is set up for that, but it is one of the most difficult things to find. Now a days we have camera scopes and things of the sort, but if you do not have one.....
    Never give up; Never surrender!

  9. #9
    Join Date
    Aug 2006
    Posts
    2,584
    The most Failures I see are caused by Humans. Whether it's a **miss adjusted thermostat, to that cute picket fence around that ugly AC unit. Or the last Service tech. giving the Unit a "shot" of refrigerant.

    **Had a Board room full of our brightest people, couple of them PHD's. They took a break and put in a call for no AC. They were quite irrate when I got there, looked at the Plain ole Mercury Bulb T-stat, it was set for heat!

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