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  1. #1

    A350 johnson control, how does it work????

    I was at a restaurant working on a york rtu. Customer was saying its to warm in the restaurant which it was 77 and the a/c wasn't working. The ambient temp was about 55. The unit has a low limit A350 control and another for compressor lock out. I know this has to have something to do with it. I bypassed the relays to get the compressors to turn on. Can anyone explain to me how these controls work???

  2. #2
    Have you checked for shorts? They have a built in feature that shuts down if detects a open or short circuit. Also have you checked to make sure the minimal set point is correct?

  3. #3
    Join Date
    Oct 2012
    Location
    Wisconsin
    Posts
    3,860
    What temp was the CLO set for? If it was set above 55 degrees, it did its job by shutting off mechanical cooling.

    The low limit powers w1 when discharge air temp drops below low limit setpoint.

    Compressor Lockout locks out mechanical cooling when outdoor air temp is below setpoint.

    There may also be an occupied relay, that will disable mechanical cooling when building is unoccupied (a1, a2 connections for thermostat)

    Also, a somewhat unrelated question but does the economizer work? Even if it was set on "D", it probably should have opened if it was 55 degrees outside.

  4. #4
    Quote Originally Posted by Mike19 View Post
    What temp was the CLO set for? If it was set above 55 degrees, it did its job by shutting off mechanical cooling.

    The low limit powers w1 when discharge air temp drops below low limit setpoint.

    Compressor Lockout locks out mechanical cooling when outdoor air temp is below setpoint.

    There may also be an occupied relay, that will disable mechanical cooling when building is unoccupied (a1, a2 connections for thermostat)

    Also, a somewhat unrelated question but does the economizer work? Even if it was set on "D", it probably should have opened if it was 55 degrees outside.
    It was set for 60, i turned it down to 50 waited about 10 minutes and still no compressors. I even tried turning unit on and off. Does that mean the n.o. contacts control mechanical cooling? What does the n.c. contacts control? To be honest i never learned how to troubleshoot the economizer. There was 24v at TH and TR and yes it was set at the D position but economizer was barely open.

  5. #5
    Join Date
    Oct 2012
    Location
    Wisconsin
    Posts
    3,860
    Is it a Sunline or Predator unit?

  6. #6
    Quote Originally Posted by Mike19 View Post
    Is it a Sunline or Predator unit?
    Its the older unit. Its not thr predator so I guess its the sunline

  7. #7
    Join Date
    Oct 2012
    Location
    Wisconsin
    Posts
    3,860
    Yeah, the older York is the Sunline.

    This is a schematic for the clo and low limit. They are optional on those, they aren't shown on the main schematic in the unit, there is an extra sticker for the kit.

    If you want to bypass the clo and low limit, just unplug both its molex plugs, and plug the wiring harness coming in right to the molex plug connected to the economizer control.

    Here is how its wired:


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