fan cycling switch..
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  1. #1
    Join Date
    May 2005
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    1,347

    Hmm

    im usually cornfused when it comes time to add a fan switch as to what parameters to use...
    lets say for example a condensing unit has a high side psi limit of 500 lbs..
    i have a feeling im setting these little doOds to come on too soon..
    i use mostly 401a, 404a...

  2. #2
    Join Date
    Jul 2000
    Location
    Guayaquil EC
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    10,249

    condenser fan cycling.......

    Set the control up to open at the pressure equivalent to 90ºF condensing temperature and close at 40 psi above that. For R404A that would be CO at 205 psig (90ºF) and CI at 245 psi.

    The 500 psig pressure limit has nothing to do with the unit operation......it has to do with the unit exploding.

  3. #3
    Join Date
    Aug 2002
    Location
    Southold.calm
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    5,376
    So Ice what about the I C M controller . I’ve used a few of these no problems so far. Also eliminates the quick on/off problems.





    http://www.icmcontrols.com/products/head_pressure.html

  4. #4
    Join Date
    May 2005
    Posts
    1,347
    thanks ice, ill jot that down..on the 500 psi thing, i knew that, and never set a head psi or fan switch by that number..
    i had set the 404a system at 150/200psi.. a bit low then.

  5. #5
    Join Date
    Jul 2000
    Location
    Guayaquil EC
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    10,249
    Originally posted by pecmsg
    So Ice what about the I C M controller . I’ve used a few of these no problems so far. Also eliminates the quick on/off problems.
    I've used them a couple of times with good results but prefer controlling directly to discharge pressure and not temperature. If you need stable control and have relatively cold winter ambients, go with a headmaster control.

  6. #6
    Join Date
    Jul 2004
    Location
    NJ
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    1,791
    I set every fan cycling control for any refrigerant to average a 110*F condensing temperature.Cut out at 120*F condensing temp.cut in at 100*F condensing temp.Whatever pressure they correspond to.

  7. #7
    Join Date
    Jun 2001
    Location
    Michigan
    Posts
    12,077
    Originally posted by wannafreeze
    I set every fan cycling control for any refrigerant to average a 110*F condensing temperature.Cut out at 120*F condensing temp.cut in at 100*F condensing temp.Whatever pressure they correspond to.
    Nuttin rong wit dat.

    I go 90 liquid, but so what. You get the idea why it needs to be on board equipment and why it needs to be set so. A couple pounds in one direction, if thats your preference so be it. Call it your signature. Thats your name on that setting.

  8. #8
    Join Date
    Aug 2005
    Posts
    831
    Originally posted by wannafreeze
    I set every fan cycling control for any refrigerant to average a 110*F condensing temperature.Cut out at 120*F condensing temp.cut in at 100*F condensing temp.Whatever pressure they correspond to.
    Couldn't settings that close lead to a lot of motor cycling in cold weather?

    I like the P66 controls, pricey and a pita to mount etc. but had very good results, even in situations where headmaster failed and I didn't want to open up the system.
    eventu rerum stolidi didicere magistro

  9. #9
    Join Date
    Jan 2006
    Location
    Near Atlanta, GA.
    Posts
    14,488
    What kind of compressor do you have? Many of the semi-hermetics are air cooled and the manufacturor requires constant air flow across the body. Check to see and if so better to use a headmaster valve and run the fan whenever the comp is on.

  10. #10
    Join Date
    Jun 2001
    Location
    Michigan
    Posts
    12,077
    I only have installed 1 p66. It was on a RTU being used to cool a computer room, of all things. That is another story. But. The need to run that unit in cooling in lower ambients found me having to mess with head pressure. What a PIA they are to install. It worked fine. But. The only thing I didn't like on my install was, I figured I'd see the head stay steady, but the fan would ramp up and down a little bit. You could see head go up and down a bit. I wanted to see a smoother ramp. I am so used to seeing freeq drives match my head settings so tight that I guess I sort of expected to see that from this. And so I was disappointed with it. But, all in all, it is serving it's purpose. I was just on that unit after 2 years, and that control is still working.

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