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  1. #1

    Fan cycling help.......

    Hello All, I am a contractor in southern California and needed some help from you professionals about installing a fan cycling switch. I installed a small custom four drawer 1/2 HP r404 system around summer time. I haven't had any problems with system until now. The customer calls and says product is freezing. The system runs only on LPC and no defrost timer. I sized condenser for 110* ambient conditions, but now that's reaching 40-55* at night and 60-70* day time is it a good idea to install condenser fan cycling switch to keep HP up? I don't want to mess with LPC settings because I don't think that's the solution. I've been in trade for 15 years, but never had to install these only troubleshoot. Any input would help, thanks in advance.

  2. #2
    Join Date
    Aug 2009
    Location
    Malden, MA
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    10
    Elite-Mech, I think intalling a headmaster would be better for the longivity of the system given the temperature swing you have there. Put a fan cycling switch in and set the cut out pressure at around 90F doesn't hurt either. If you don't have any sort of HP control, you'll be replacing that compressor pretty soon. Also, is this a cooler or freezer? It sounds like a freezer (404A) and you don't have a defrost timer? Strange. Good luck.

  3. #3
    Quote Originally Posted by cuchien View Post
    Elite-Mech, I think intalling a headmaster would be better for the longivity of the system given the temperature swing you have there. Put a fan cycling switch in and set the cut out pressure at around 90F doesn't hurt either. If you don't have any sort of HP control, you'll be replacing that compressor pretty soon. Also, is this a cooler or freezer? It sounds like a freezer (404A) and you don't have a defrost timer? Strange. Good luck.
    Its a cooler

  4. #4
    Join Date
    Mar 2007
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    wedged in freezer shelf
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    6,664
    If it is only on LPC it would reach cut out sooner with low head.
    If you are going to change something I'd go with a tstat
    Is it only one evap?

  5. #5
    Join Date
    Jul 2003
    Location
    Elizabethtown ,KY
    Posts
    209
    Sure you could install a fan cycling switch in there. I try to maintain 90- 100 degrees condensing temperature. A head master would be a better answer. I don't like the temperature /pressure swings with fan cycling, but it will serve the purpose. So I take it that this has a remote condensing unit? Or is this a self contained box outside? Typically, running a condensing unit in low ambient conditions without low ambient controls of some sort ,results in the unit running as though it were low on charge. The result with pressure controlled temperature is that usually the box won't get cold enough, because one the pressure control shuts off early due to the low charge like situation and or the evaporator is not fully effective for the same reason. Are you sure there are not other reasons?
    On larger equipment, I've all but abandoned fan cycling in favor of electronic modulation of the condenser motors.

  6. #6
    Join Date
    Oct 2009
    Location
    Raleigh, NC
    Posts
    794
    If the head is dropping too much at night, I can't see why it would freeze product?

  7. #7
    Join Date
    Oct 2011
    Location
    Chicagoland Area
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    4,575
    Quote Originally Posted by MicahWes View Post
    If the head is dropping too much at night, I can't see why it would freeze product?
    Agree. If anything, I think it would short cycle.
    Officially, Down for the count

    YOU HAVE TO GET OFF YOUR ASS TO GET ON YOUR FEET

    I know enough to know, I don't know enough
    Liberalism-Ideas so good they mandate them

  8. #8
    Join Date
    Jul 2003
    Location
    Elizabethtown ,KY
    Posts
    209
    Quote Originally Posted by 2sac View Post
    Agree. If anything, it would short cycle
    Essentially that's what I said, with a little more info

  9. #9
    Join Date
    Oct 2011
    Location
    Chicagoland Area
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    4,575
    Quote Originally Posted by jimmytee View Post
    Essentially that's what I said, with a little more info
    I like to keep it simple LOL
    Officially, Down for the count

    YOU HAVE TO GET OFF YOUR ASS TO GET ON YOUR FEET

    I know enough to know, I don't know enough
    Liberalism-Ideas so good they mandate them

  10. #10
    Join Date
    Mar 2013
    Location
    swan valley idaho
    Posts
    727
    it would work and be easy to install. i have them on walk ins in jackson wy and see 10 to 20 below zero nightly.

  11. #11
    Join Date
    Sep 2002
    Location
    Virginia
    Posts
    3,156
    the easy fix is adding a fan switch to turn fan off at 200 psi and lower

    Sometimes it gets confusing when setting it up , because you want it to come on 200 and higher

  12. #12
    Join Date
    Mar 2013
    Location
    swan valley idaho
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    727
    on 200 off 250 works pretty well

  13. #13
    Join Date
    Jun 2005
    Location
    Las Vegas NV
    Posts
    1,152
    For a typical 4 drawer under counter refrigerator I think the 1/2 hp system is oversized. Added to that, you're gaining about 35% btuh capacity at a 50 degree ambient versus a 110 ambient. The LPC is probably set at a cut out just above freezing the product during higher ambient temperatures.

    With that said, I would think that there is too much sub-cooling at the lower ambient temperatures. If it's a TXV system then the TXV will be oversized even though the pressure drop across the valve is less. The extra subcooled liquid refrigerant and the LPC settings are probably what's causing the freezing of product.

    I'd install a FCC and temperature control.

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