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  1. #1
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    Mar 2013
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    medium temp walk in freezing product

    looked at a medium temp walk in today running to cold. found it was getting to about 30 degrees. has a johnson control a419 temp control. checked it against my fluke 52 digital. it seems to be reading about 5-6 degrees off actual temp. ohmed out sensor per manual. got 900 ohms at 40 degrees. right on spec. so i guess that means temp control is bad? sensor ohms correct but temp control reads 44 when actual temp is about 38. box about 10 yrs old, sensor never moved or anything like that.

    also low suction(35 psi with r22) at 35 deg. box, while very low sh, about 1-3 degrees. sight glass clear, fans both on, im thinking coil must be dirty inside restricting airflow. any help appreciated. thanks

  2. #2
    Join Date
    Mar 2009
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    Ya the suction pressure seems a bit low, but it seems like you are on the right track to me with the cold control. Are you planning on just replacing it or so you want to try to make this one work? If so it's time to put your warm clothes on and adjust it like you would a manual one by waiting on it to make setpoint.

  3. #3
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  4. #4
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    Oct 2011
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    Sounds like you're on the right track. Check the settings and dip switches on the a419 before you condemn it. Lock out the new control or the reprogramed control, whichever you find it to be. Is the box cycling on it's own from the control? Is there a chance of a sticking solenoid?
    Officially, Down for the count

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  5. #5
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    Mar 2013
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    ya -all for changing it out, just haven't worked with the a419 much, and want to diagnose it right. like i say sensor ohmed right, but sensed temp is off about 5-6 degrees. there is no re-calibration or anything is there?

    it does cut in and out correct -example i set to 40 with a 4 degree diff. it came on at 40, off right at 35. Its just actual temps were 35-29.

  6. #6
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    Quote Originally Posted by kklobas View Post
    ya -all for changing it out, just haven't worked with the a419 much, and want to diagnose it right. like i say sensor ohmed right, but sensed temp is off about 5-6 degrees. there is no re-calibration or anything is there?

    it does cut in and out correct -example i set to 40 with a 4 degree diff. it came on at 40, off right at 35. Its just actual temps were 35-29.

    If it is set for 40, then it would shut off at 40 then back on at 44.

  7. #7
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    Mar 2013
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    swan valley idaho
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    yes comp. does cycle on and off, relay light on control goes on/off, just abou 5-6 degrees off.

    on a separate note the low pressure, with very low superheat could only be lack of airflow correct? i'm thinking coil packed with crud inside? had to leave before they would let me clean it properly.

  8. #8
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    ryan- cut in was 40 with a 4 degree diff.

  9. #9
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    Sep 2008
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    Western PA
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    Quote Originally Posted by kklobas View Post
    on a separate note the low pressure, with very low superheat could only be lack of airflow correct? i'm thinking coil packed with crud inside? had to leave before they would let me clean it properly.
    *assuming* a draw-though type evaporator...

    Feel airflow coming out of the fans. If it is coming straight out, then your coil is likely clean.

    If it is coming out at an angle, then you needs to clean it.

  10. #10
    Join Date
    Feb 2006
    Location
    Phoenix,AZ
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    2,877
    Quote Originally Posted by ryan1088 View Post
    If it is set for 40, then it would shut off at 40 then back on at 44.
    I think there's some jumpers on it that you can have it cut-in at set point or cut out at set point. Take your pick!

  11. #11
    Join Date
    Aug 2007
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    Southern,Ca
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    510
    This may be a stupid question but are you sure that the sensor is not located too close to the coil? Where is it located, I like them on the back wall behind the coil mounted on the wall but not touching it..

  12. #12
    Join Date
    Aug 2007
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    Southern,Ca
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    510
    Quote Originally Posted by KB Cool View Post
    I think there's some jumpers on it that you can have it cut-in at set point or cut out at set point. Take your pick!
    Yes those jumpers do exist, I found them the hard way... I couldnt figure out why the control was cutting in when it should cut out, I figured it out eventually,

  13. #13
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    Mar 2013
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    swan valley idaho
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    yes on jumpers. sensor on back wall behind coil, about 2 feet away. it does touch wall, but hasn't been messed with in years. Does it sound like time for a new control or is there any testing left to do. thanks for all the suggestions

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