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Thread: A/C Question

  1. #1
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    A/C Question



    Hi Guys,

    Question :-

    If a/c systems, especially old ones without a defrost freeze up and cause water leaks when set below 20 degrees why to manufactures allow you to set the stat to below it (17 in some cases)


    Regards

    Raymond



  2. #2
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    Re: A/C Question

    Raymond, if it freezes up then something is wrong with it or it is operating outside its' design parameters.

    They generally start freezing if the airflow reduces when the filter gets blocked or someone hangs their coat over the inlet, or the fan is slow due to old age; you can also have similar problems if it starts over condensing due to lack of fan speed control.

    The person who makes the 'stat doesn't always know what service it is going to be used for and if it was only made to go don to 20C then some fool would want it down at 17C.

    Other than that I haven't got a clue, what is the answer ??
    Brian - Newton Abbot, Devon, UK
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    Talking Re: A/C Question

    As far as I know then they should not be freezing up. It's all down to the evaporating temperature in the system. On the newer ones it isn't unusual for the evaporating temp to be below freezing especially in lower ambient temperatures. A/c applications are usually designed to run at a higher evaporating temp and therefore a slightly higher temperature than lower temp applications. As far as I know if it is freezing then there's usually a fault. Clogged filters, short of charge, problem with indoor fan/thermostat etc. Usually they don't have thermistors as far as I know to measure coil temperature and so on. I would go straight back to basics and start from there, but apart from that I'm not sure why the thermostats can be set so low-but isn't that the room temperature? Surely this has nothing to do with the coill temperature. For instance if the evaporating temperature is say 2 degrees C on R22, then you would have a suction pressure of 62psig, the coil will be running cold enough to bring the setpoint down without freezing. If the thermostat allows very low setpoints, then change it-they aren't like the newer ones that allow you to set dipswitches to contol selection ranges etc. I had the same problem recently with a job. The problem was being caused by the fact that the compressor still cycles for a little while after the setpoint is reached, so overnight it was icing up. In the end we had to fit a head pressure control (not that relevant I know)

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    JAmes
    Last edited by iceman007; 24-08-2004 at 09:34 AM.
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    Re: A/C Question

    Hi Raymond.

    I'm not sure what you mean by old AC systems but if you have a problem of freezing evaporator coil, there are two ways that I use to protect them.
    One, is to add a therostat, a gigital one in serie with the original, the probe is in the coil, set on 1C to stop the compressor or SV.

    Second, is the American way. the real thermostat is in the plant room and all the others are fake.
    You will be surprised that people will feel colder if they turn the fake one down.

    Chemi

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    Re: A/C Question

    Second, is the American way. the real thermostat is in the plant room and all the others are fake.
    You will be surprised that people will feel colder if they turn the fake one down.
    I like that Chemi - never thought of it myself but it could solve many a problem I've had lately ( especially when you have both guys and galls in the same office

    If a/c systems, especially old ones without a defrost freeze up and cause water leaks when set below 20 degrees why to manufactures allow you to set the stat to below it
    Raymond

    I hear what you are saying as I fitted a few systems in a hotel gym in Bristol and they wanted the stat to go down to 16 (Daikin) but this one didn't go below 20 and they were pi**ed off. Seems that the controller was designed for Japan and their lowest set point was 20 due to the ambients in Japan. Anyways, a new circuit board sorted it.

    If you have an old mechanical A/C system I bet it's got either on Eberl or OEM mechanical stat that goes from 15 to 30C - basically a stat for all seasons

    I bet you wish you could fit a Ranco - Don't really know the answer to your question but I can sympathise with your problem, just like I bet you wonder why they put loads of buttons on the latest controllers (Mitsi, Fuji, Hitachi, Daikin etc ) which leave it wide open for the uneducated office residents to play with that make our life a misery (it's not COOLING? - no because you've got it in HEATING at 32C !! )

    Obviously, any A/C that freezes has a problem as they are all designed to evaporate above 0C.

    Stay calm - it's nearly WINTER
    Last edited by frank; 24-08-2004 at 08:21 PM.
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