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  1. #1
    Join Date
    Apr 2009
    Location
    Hernando, MS/Memphis. TN
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    3
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    Trane RTEM Economizer 2-10 VDC Override

    For a little background, I have a job coming up where we are replacing existing programmable stats with Viconics/Schneider Electric SE8650s with WiFi cards. This will give the customer an inexpensive BACnet interface to their existing Niagara N4 BAS without running cable for BCI-I cards. This part is straightforward.

    The customer insisted that we needed to price taking over control of the economizers. I knew this would be a challenge and recommended against it initially, but the customer wouldn't listen. Because I couldn't get to the site before the proposal had to be turned in (they surprised us and gave a one day window to complete), I threw a high enough number at it and figured we would be good, as these are small package units. Our money situation is likely fine, but we are now severely short of time because this has to be done by 12/31 and we have been flooded with new work, most of which also has to be done by 12/31.

    I am currently in a walking boot, so I had to send a service tech to the roof to look at these units and what we found would be difficult to work with in terms of space and accessories to retrofit. At the very least, it would be time consuming and that's a luxury I don't have. However, we did notice that the RTEM factory Trane Econ Controller on these units has a terminal marked 2-10 VDC Override.

    I figured we could just leave these Econ controllers in place and use them via this override with one of the AOs built into the SE8650. However, I have not been able to verify that this input does exactly what I'm looking for. I have been scouring Google and this site and have looked through several manuals and haven't found anything yet about the sequence and functionality for this particular input.

    Before going to the site and doing a trial run that may end in failure in front of the customer (this guy is nosy and would be looking over our shoulders), I thought I would reach out here and see if anyone else has made use of this 2-10 VDC Override before. Is it as straightforward as sending it a signal to control the Min OA Damper Position and the Econ operation at all times, or am I missing something? Any insight on this or any other easy alternatives would be appreciated.

    Thanks in advance.

  2. #2
    Join Date
    May 2018
    Location
    VA/DC
    Posts
    291
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    on the economizer motor. you moved the control head, its one star head screw. then remove the base plate. you will see on the motor there is a 24v + common and a 2-10 in. connect there.

    The common terminals for power and 2-10 are the two closest to each other. Ohm them out to be sure though. I have done this on multiple trane units when I want full control.

    I know there are inputs on the head. I have never tried them.

    Once you take off the head and cycle power the main rtum no longer sees the economizer control and things it doesnt have one and goes straight to the compressor for first stage in cooler weather.

  3. #3
    Join Date
    Nov 2011
    Location
    East Side
    Posts
    7,078
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    that module should be the Honeywell W7340 Premium western. it should have Modbus.....can you not connect to that?

    refer to honeywell doc# 63-2569. all the diagrams show the 2-10VDC as the connection directly to the motor inputs, but none of the honeywell diagrams show an external connection to those terminals.


    The only problem I see removing the module is you now have to install another enthalpy sensor for the control system. do any of the units have exhaust fans?

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