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How should I switch an air conditioner off?

  1. May 26, 2012 #1
    I have heard from not very educated 'technicians' who installed my air conditioner, that I must first switch off the compressor of the AC by switching it to fan mode, and after some time, switch it off, to avoid some kind of collection of cold air inside it. I kind of followed it for the time being I had a window AC, but I've entirely abandoned doing this since I got a split AC. Am I damaging my air conditioner in doing this?
     
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  3. May 26, 2012 #2
    And when your starting capacitor runs out of electrons, you will have to buy a box of electrons to refill it.

    I heard that equally silly statement from another technician. I just smiled and thanked him for his advice. My dad taught me well that everyone has a constitutional right to be ignorant, and that if they choose to exercise their right I should let them be.
     
  4. May 26, 2012 #3

    mfb

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    Maybe this advice is related to condensed water, which could be produced at cold surfaces if you don't continue to blow air over them (and therefore keeping their temperature up). However, I have no idea how serious that could be.
     
  5. May 26, 2012 #4
    The best way to stress your air conditioner compressor motor is to shut it off and restart right away. If you do that enough times the motor overheats and blows. The motoer would be trying to restart against high pressure fluid that hasn't had time to flow through the capillary tube and lower the pressure. More times you hear of fridges that have been ruined by a power outage than air conditioner units.

    My best guess is that they have skewed that factor into telling clients to run the fan. A case of a little bit of science being stupid ( rather than dangerous ). Well dangerous in the fact that they might try to use it aganist you if you didn't follow their instructions and you would be at fault instead of the unit if it malfunctions under warranty.
     
  6. May 26, 2012 #5
    My AC controller is one of those that has ICs and programs...

    Whenever it changes from running the AC to turning it off, it first stops the compressor and leaves just the fan to blow the remaining cool air out of the conduit tubes for about 90 seconds, then turns off the fan.

    This is supposed to do two things, one is get the remaining chilled air in the attic conduit tubes moved into the living area, second is to prevent having chilled air resting in the conduit.

    I suppose the first reason is to make the most efficient and least costly use of the chilled air in the conduit - over the years it might add up a little.
    The second reason is to help prevent condensation in the conduit, which can lead to various problems including growing mold and sludge, bad smells, health risks, integrity of the conduit and its fittings to the vents, etc...

    Having the compressor turn off with a lead time before the fan makes sense to me. I'm not understanding the arguments about switching the compressor on and off... in normal use the system will do that periodically anyway based on the thermostat.

    Maybe the period of just running the fan after compressor cut off also helps prevent the condenser unit from freezing up? I'm not an HV/AC expert, but when your condenser freezes up the immediate fix is to just run the fan for a while to clear it (and then figure out why there is not enough air flow or whatever that is causing it to do that)...
     
  7. May 26, 2012 #6
    GM used to have a problem on a few of their models with AC odor. When the car was shut off with the AC running water would condense on the evaporator and then warm up as the interior of the car warmed up. This + pollen from the outside air would allow mold to grow on the evaporator eventually causing an unpleasant odor. The fix for this problem was a software update to the HVAC control module that would turn the blower fan on for 30 seconds several times between 30 and 45 minutes after the car was shut off. This was to move dry air into, and wet air out of the evaporator case to carry moisture away.

    The advice you got from your HVAC technician may be intended to accomplish the same thing.
     
  8. May 26, 2012 #7

    russ_watters

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    You have a thermostat: use it, it is smarter than that tech.
     
  9. Oct 8, 2012 #8
    I think you shouldn't turn it off. I think you should just turn it up to 78 or 80 and then turn it down when you get home. Get one of those energy efficient thermostats so all you have to do is program it. You could program it to turn it down about 30 minutes before you get home so you won't be dying of a heat stroke waiting to cool.
     
  10. Oct 9, 2012 #9
    Hmm, the technician's explanation makes sense to me. You'll get less mildew in your AC if you let it dry out first.
     
  11. Oct 9, 2012 #10

    sophiecentaur

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    Turning off your air con in motor cars, a few minutes before the end of a journey is recommended in several car manuals I have read - for the 'mildew' reason. Some service stations offer 'health checks' and de-contamination of your system.
     
  12. Oct 9, 2012 #11

    russ_watters

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    This is an old thread, but to expand on my previous post:

    This is a function that AC units already do, so it is silly to do it yourself, manually. In addition to drying the coil, leaving the fan on for 15-30 sec after shutting off the condenser also pulls a little more cooling out of it, saving energy.
     
  13. Oct 10, 2012 #12

    sophiecentaur

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    That makes sense. In a domestic system, with a constant supply of power, it's easy to build in that function - unlike a motor car, which has no idea of when you are going to stop the engine and remove the ignition key. It would be easy to listen to what the domestic AC actually does when it is turned off 'properly'.
     
  14. Oct 10, 2012 #13

    russ_watters

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    Just because you turn the ignition key to "off", doesn't mean the car can't still do whatever the manufacturer wants it to do. My headlights and radio stay on, for example and my power windows still work. My seat used to retract, but I turned that feature off.

    If this were important, they would do it. For a car, it may simply be that the heat from the engine burns off any condensation on the cooling coil after you shut it off.
     
    Last edited: Oct 10, 2012
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