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  1. #14
    Join Date
    Oct 2011
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    Chicagoland Area
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    Now we know it's hot gas defrost. If you know how hot gas defrost works. You should be able to determine if this is the problem or you need to look elsewhere
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  2. #15
    Join Date
    Oct 2012
    Posts
    10
    Found settings on defrost clock to be adjusted improperly, as well as the fan cycling control. Found my low side gauge to be faulty and replaced with new one. subcooling was around 7*f and superheat around 30*f. added some refrigerant, adjusted settings of defrost timer and fan cycling control and unit is operating properly at this time. Unit did pump down, and to rephrase the unit going into defrost 3 times, i meant that the cond. fans went on and off 3 times within the couple hours i was there. My boss told me to check the settings on the fan cycling control, defrost timer, check for restrictions in the line, and charge. found no restrictions, or temperature differences in suction or liquid line, and issues listed above were corrected with the bosses guidance.

    Questions/ Concerns at this point are:

    -2sac said what's wrong with ice on the txv. I've read that if there is water in the refrigerant (say on the first hot day, drier turns a drop or two of water loose), it will freeze in the expansion valve, and stop the refrigeration circuit. mis-understood sentence and interpreted it as ice on the txv indicates moisture in the system. after further reading, i understand that its moisture IN the refrigerant that will stop the expansion, not ice ON the txv.

    -what is the general rule of thumb for setting a defrost clock, and what do you do if unit is still not defrosting properly? Do you add 5,10, or even 15 minutes to that defrost cycle?

    - If you lengthen the time of defrost, do you have to worry about perishables thawing during that time? does anything need to be adjusted as far as low pressure controls?

    -how do you properly set a fan cycling control? (and for learning purposes we'll say with an r-22 system)

  3. #16
    Join Date
    Sep 2011
    Location
    Fayetteville, NC
    Posts
    130
    -2sac said what's wrong with ice on the txv. I've read that if there is water in the refrigerant (say on the first hot day, drier turns a drop or two of water loose), it will freeze in the expansion valve, and stop the refrigeration circuit. mis-understood sentence and interpreted it as ice on the txv indicates moisture in the system. after further reading, i understand that its moisture IN the refrigerant that will stop the expansion, not ice ON the txv.

    -what is the general rule of thumb for setting a defrost clock, and what do you do if unit is still not defrosting properly? Do you add 5,10, or even 15 minutes to that defrost cycle? There is no rule of thumb per say. It all depends on how the customer uses the box. D

    - If you lengthen the time of defrost, do you have to worry about perishables thawing during that time? does anything need to be adjusted as far as low pressure controls?

    -how do you properly set a fan cycling control? (and for learning purposes we'll say with an r-22 system)

    For defrost it all depends on how often the door is open. Customers will always tell you that they close the door but you will find out with time that everyone LIES! Depending on the conditions at the store you may see a unit in that only defrosts 3 times a day for 25 minutes. That same unit in a humid environment will need four. Don't consider the job done till you check up on it. I don't know how many times I go to a job at a local fast food place and arrive and see that the freezer door is propped open while they do inventory. Leaving a freezer door open in North Carolina in the summer times will frost up an evap in no time. You have to adjust and modify accordingly.

    For the thawing,,, I say no. If you box is down to temp the effects are negligible. Of course if there is a deforst going on and they leave the door propped open you may have a problem. It all depends on the environment

    For fan cycle switches set them to simulate a 90 degree day. Ignore the gauge on the low pressure switch. Always use your manifold to set em. May take you a lil while to get it figured out but once you get the first one you will find that the rest are a breeze!

    Just a thought, don't be afraid to leave an invoice open. It gives you the chance make sure the changes that you have made are correct and working in the customers best interest.

  4. #17
    Join Date
    Oct 2011
    Location
    Chicagoland Area
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    Rule of thumb for a defrost clock. 4 defrosts per day timer on clock should be set for no longer than 45 min BUT you should have a temperature termination switch on the coil. The timer on the clock is usually used as a backup method to terminate the defrost.

    Food takes along time to thaw.

    As far as the LPC, What is ts purpose? A safety? A temperature control?

    Fan cycle control? Doesn't matter what referigerant is used. Time to pull out the PT Chart. You're in A/C, What condensing temp is ideal in a properly charged running unit under "ideal" conditions? Compressors are designed to work to their potential under these conditions. It's an easy answer. Anyway, that # should be in between your cut in and cut out of the control.
    Hope this helps. Can't get into too much detail on an open forum.

    EDIT If the defrost os too long, water droplets will form on the top and sides of the box and then freeze
    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

  5. #18
    Join Date
    Sep 2011
    Location
    Fayetteville, NC
    Posts
    130
    2sac,,,,, I wish you were my boss

  6. #19
    Join Date
    Oct 2011
    Location
    Chicagoland Area
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    4,508
    Oh?
    please explain
    Officially, Down for the count

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

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    Liberalism-Ideas so good they mandate them

  7. #20
    Join Date
    Sep 2011
    Location
    Fayetteville, NC
    Posts
    130
    just for the fact that I read your posts. If I every was in a bind I knew I could call you and you would give me information that would actually help me.

  8. #21
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    Oct 2011
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    Chicagoland Area
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    Glad to help. I'd be a terrible boss though. I like to work 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

  9. #22
    Join Date
    Sep 2011
    Location
    Fayetteville, NC
    Posts
    130
    let me rephrase that. My senior tech. And yes,,, I like to work too.

    I just hate cleaning up messes left by my "senior" tech.

  10. #23
    Join Date
    Oct 2011
    Location
    Chicagoland Area
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    It's called job security
    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

  11. #24
    Join Date
    Oct 2012
    Posts
    10
    appreciate all the help guys. back to the fan cycle control question though, say you're using r-22, looking for a condensing temp of 100*f, you're saying use that, converted to pressure(196psig), you want to use that as number as your differntial? and what would you set your high even at 200*f? A bit confused

  12. #25
    Join Date
    Oct 2012
    Posts
    10
    I understand that when the control reaches a certain pressure(high event), it turns the fan on, and when the pressure drops to a certain point(low event), it turns the fans off. i get that part. what i don't understand is how you arrive at those set points

  13. #26
    Join Date
    Oct 2011
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    Chicagoland Area
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    The control probably has a minimum differentila of 40-60psi so if 196psi is your target, it should be somewhere in the middle. You would set the control to CO at 180ish CI 220-230ish. Doesn't need to be exact. A headmaster is a more efficient way to control liquid going to the txv
    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

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