Results 1 to 5 of 5
  1. #1
    Join Date
    Jun 2019
    Posts
    7
    Post Likes

    Carrier UPC Open + space temp sensor; "controlling space temp" reporting constant 88

    I'm working controls on a job with two Carrier RTUs with UPC Open controllers. Both have identical Carrier 10K space temp sensor installed, wired identically. Measuring voltage across the terminals, both read ~2.3-2.4 V DC; detaching the sensor leads at the unit and measuring resistance across the sensor, both read ~11-12 Kohm.

    However, one unit is correctly reporting the space temperature on both the "spt" (Space Temperature) point and "space temp" point (Controlling Space Temp), while the other unit is reporting correctly to "spt" but a constant 88 degrees on "space temp" -- meaning I can't control to space temp on that unit.

    Any idea why the unit/controller is holding the Controlling Space Temp point at 88 rather than matching the Space Temperature point?

  2. #2
    Join Date
    Aug 2014
    Location
    DMV
    Posts
    77
    Post Likes
    Quote Originally Posted by skreidle View Post
    I'm working controls on a job with two Carrier RTUs with UPC Open controllers. Both have identical Carrier 10K space temp sensor installed, wired identically. Measuring voltage across the terminals, both read ~2.3-2.4 V DC; detaching the sensor leads at the unit and measuring resistance across the sensor, both read ~11-12 Kohm.

    However, one unit is correctly reporting the space temperature on both the "spt" (Space Temperature) point and "space temp" point (Controlling Space Temp), while the other unit is reporting correctly to "spt" but a constant 88 degrees on "space temp" -- meaning I can't control to space temp on that unit.

    Any idea why the unit/controller is holding the Controlling Space Temp point at 88 rather than matching the Space Temperature point?
    Did you check to see where the control source was set to? I believe the is a point that allows you to select this and it can be hardwire or a network set point. You have to have a hardwired sensor for the unit to run, but can have a network space temp write to the board to control to a different value, which is what it sounds like here.

    Just and FYI if you do have it writing the space temp from a network point you have to right to it using very specific time intervals and only input 16 I think. Carrier has odd rules for this. When you do write to it the point will blank out to a different value once it accepts the change until the next interval writes it again.

  3. #3
    Join Date
    May 2018
    Location
    VA/DC
    Posts
    284
    Post Likes
    its possible that the point got locked during unit start up so the cooling would run. Does the job have an I-vu or equipment touch? you can fix it with that. priority level 16 is the only communication level for carrier.

    if you are only bacnetting in. you can verify by checking the following.. ai_10 and see what it says. or AI:1010 same point though. I do carrier so I have never bacnetted into a rtu open to see exactly whats there. See what the value is and if you can unlock it. then look for spt_type set it to t55 This will also be MSV:9001 you want to send that a value of 1

  4. #4
    Join Date
    May 2018
    Location
    VA/DC
    Posts
    284
    Post Likes
    im rereading your first post as i am logged in live to a site.
    reference name space temp is the final output for the space temp, nothing is after it in the program.
    SPT is a typical wall sensor and the 10k goes to input 10.

    But basically if the space_temp shows 88 and the spt does not ( reads actual room temp ) then there has to be a locked point. and the sensor choice is not T55 or and input of 1

    check and report. email me if needed.

  5. #5
    Join Date
    Jun 2019
    Posts
    7
    Post Likes
    Thread Starter
    I contacted the Carrier rep who was handling the commissioning of the unit; here's what he had to say:

    I believe you are saying that the space temperature SPT point AV:137 is reading accurately, but controlling space temp point SPACE_T point AV:2007 is reading a constant 88°.

    If SPT isn’t reading, check the following: Under Configuration >UNIT>SENS>SPT.S, enable the space sensor by setting SPT.S to ENBL.

    Since the unit is not controlled via space temp, the controlling space temp point defaults to a value. Evidently that value is 88°. This point AV:2007 is not used to control anything.

    The unit is controlled via return air temp. If you were to look at controlling return air temperature RETURN_T point AV:1030 it should give you the actual temperature the unit is looking to for control of setpoint.

    I don’t believe you can change rat to spt control over bacnet. However, at the unit, it's a simple change; the type of control is configured under Configuration>UNIT>C.TYP. Set C.TYP to 1 (VAV-RAT) for return air sensor. Set C.TYP to 2 (VAV-SPT) for space sensor. Or C.TYP to 5 (SPT MULTI)
    I haven't been back out to the site yet, so I haven't been able to check that out.
    Last edited by skreidle; 09-26-2019 at 10:19 AM. Reason: Formatting

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •