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  1. #1
    Join Date
    May 2012
    Location
    Germantown, MD
    Posts
    38

    Trane XV80 & IAQ stat

    Had our system replaced last week with a 3.5 ton XR13 AC, 80k XV80 furnace, and Honeywell IAQ stat. I was reading the various manuals and looking at the settings (I am a nerd mechanical engineer and like to know how things work) and found a few things that seemed off, wanted to get some insight before the tech comes back later this week for a checkup (the furnace makes a rattling/clunking noise at fan start up). System maintained temp at 75 deg and humidity ~50% during our ridiculous heat of the past few days FWIW.

    Dip switches S4-1 and 2 are both set to On and it seems the ComfortR profile is active whenever a cooling call is made.

    The IAQ is set up for dehumidify with AC (379=1). The system definitely turns on the AC if the measured humidity goes 5% higher than the setting. Overcooling limit is set to 3 deg (383=3) and this seems to work correctly too. What is not clear is if the wiring is set up correctly to run the blower at the reduced speed for dehumidification. Here's what I see inside the EIM:
    From IAQ:
    1 - red
    2 - white
    3 - blue

    From EIM:
    C - white to compressor, blue to furnace
    R (hard jumpered to RC and RH) - red to furnace
    W1 - white to furnace
    W2 - black to furnace
    Y - red to compressor, yellow to furnace
    G - green to furnace

    All other terminals are unused. At the furnace I see the following:
    Y - yellow
    W - white
    W2 - black
    R - red
    G - green
    C - blue
    Neither O or BK are connected, nor are there any jumpers. From what I can tell by reviewing older threads, the install manuals, and a little ComfortR "pocket guide" somebody posted here, there should probably be some additional wiring. Per the IAQ manual, in the EIM it seems that R should be jumped to DHM1, which should then be wired to BK in the furnance (also see references in other docs to jumpering R and BK in the furnace which I believe would net the same result). Then per the furnace install guide note 10, "A jumper must be placed between 'R' & 'O' to enable the 'BK' circuit or enhanced mode (ComfortR). This 'R' to 'O' jumper must be in place for humidistat dehumidification and proper blower operation with a two step scroll compressor." Don't have a two step compressor but the note about ComfortR is confusing because it seems to be working without this one. Then per the pocket guide (note 2 under "Air Conditioner with Gas Furnace") there should be a jumper between Y and O. Apparently different instructions have me confused

    Additionally, some of the dip switches are confusing. Note 9 in the furnace install guide states "...S5-2 switch must be set in the 'Off' position if humidistat is used. The 'S5-2' switch must also be turned to 'Off' when applying an airflow command signal to 'BK'." The S5-2 switch is actually set to On. I guess since the wiring described above isn't there this is "correct" for the time being?

    Last, for 2 stage heating - the wiring looks correct per the manuals (EIM W1 and W2 wired to furnace W and W2). Dip switches S7-4 are all Off, so I think that means no 2nd stage heat delay (correct for stat control of this feature?) and the default 90 second heat off delay. But then in the stat, it appears to be set for 1 stage heating - 176=1 and option 250 (CPH for 2nd stage heat) does not appear.

    So, it appears that both the dehumidification and 2-stage heating features are setup sorta half correctly, and that while ComfortR is definitely working I saw a few references to jumpers that should be in place that aren't. Any thoughts would be greatly appreciated, want to make sure this thing is set up correctly.

    jeff

  2. #2
    Join Date
    Aug 2007
    Location
    Northern VA 38 degrees N by 76 degrees W
    Posts
    5,058
    Jeff you are on the right track, follow the steps and notes that you have stated and have them install jumpers and feed the furnace BK terminal from DUHM from the controller.

  3. #3
    Join Date
    Aug 2007
    Location
    Northern VA 38 degrees N by 76 degrees W
    Posts
    5,058
    Send me an Email it is in my profile, and I will forward you a book on the dip switch settings and there functions

  4. #4
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,914
    Comfort-R doesn't work if O is not getting 24V to it.
    Without the jumper to O, all you get is 50% fan for one minute, then 100% fan.

    Comfort-R is 50% for 1 minute, 80% for 7.5 minutes, then 100%.
    If more government is the answer, then it's a really stupid question.

  5. #5
    Join Date
    May 2012
    Location
    Germantown, MD
    Posts
    38
    Mark,
    I'll double check the wiring but I'm almost certain there's no jumper to O and that I'm still seeing the profile you describe. Starts slow for a minute, then speeds up, then at the ~8 minute mark it speeds up again. Then after cooling call ends and the outdoor unit stops it goes down to a slow speed for a few minutes. Will report back after I check it out.

    Jeff

  6. #6
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    What your describing is Trane "Comfort-R" ramping profile.

  7. #7
    Join Date
    Jul 2006
    Location
    Virginia
    Posts
    4,615
    Its not wired for dehumidify on demand

  8. #8
    Join Date
    May 2012
    Location
    Germantown, MD
    Posts
    38

    update

    Here's an update:
    Mark - you were correct (naturally), there was a jumper from R to O, somehow I missed it. It's there clear as day.

    The tech who came by to check out the "rumbling" upon fan motor start (he did something that alleviated that) was not familiar with wiring the IAQ and XV80 for DOD. He seemed to know all about how to set it all up if there's a 2 stage compressor but doing it with a single stage was new to him. So we got it wired up per the discussion above (RH to DHM1 on the EIM, DHM2 to BK, dip S5-2 to off, the aforementioned R to O jumper already in place) and it does seem to be working now.

    I fooled around with the humidity set point while the system's been running and it clearly slows down the fan if the setting is below the actual. Once you put the setting above the actual, it speeds right up. It won't turn on the AC independent of a cooling requirement unless the set point is over 5% greater than the actual, which is how it was behaving before.

    I still have ComfortR enabled. I like the ramp up and down, as it makes the system coming on and off less noticeable. We also have a 4 ton coil with our 3.5 ton compressor, and our area tends to be humid so I figure the additional CFM reduction over that first 8.5 minutes can only serve to help. Possibly some efficiency loss but I'm assuming it'd be pretty marginal and we don't spend a ton each year on AC bills anyway. The install guide for the furnace indicates about 1350 CFM in the 3.5 ton/normal configuation, so two 20% reductions from that gets it down to ~865 cfm. Assume it's safe to operate in this manner? Thanks,

    jeff

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