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  1. #1
    Join Date
    Jan 2017
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    Trane short cycling?

    Trane XL18i, 4 ton
    TAM7 air handler
    XL624 Thermostat
    House is a 2200 sq ft rancher built on a crawl space in 1988 so walls have minimal insulation but attic has been upgraded above standards.

    Unit is only about three years old and was just serviced by the installer due to frost buildup issues. They replaced the defrost board and seems to have fixed that problem but there remains what I think is a short cycling issue.

    So here is how it typically goes. At bedtime, we drop the heat in the house to 64 from the daytime setting of 67. Makes for better sleeping. Unit shuts down until around 0100 when the house temp drops to a point that the heater comes on. It will run for approximately two minutes then shut off for approximately 10 minutes. It will repeat this cycle through most of the night until we get up in the morning and raise the thermostat setting to 67 again. The installer is telling me it shouldn't be doing that, that it should run a minimum of 12 minutes when it does come on. Obviously, they aren't coming out at 0100 to troubleshoot the unit when it is acting up but by the time they are coming to work in the morning the thing seems to be working normally, even if we don't raise the thermostat setting in an effort to repeat the "problem".

    So my question is, is the unit working correctly? Gotta believe the short run times are not good for the unit or the electric bill. Could it be that there is enough thermal mass in the structure holding heat so that when the house finally cools enough for the unit to come on that it only needs to run a short time before it comes up to the thermostat setting? Keeps my wife awake at night worrying which is not good for a whole lot of reasons.

    Appreciate any insight you can offer.

  2. #2
    Join Date
    Aug 2009
    Location
    Beatrice, NE
    Posts
    7,324
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    The XL-18i is a 2 stg unit. It sounds like the thermostat is running on cycle time rather than temperature. How long does it run after the house is at temperature? How long does it run in the summer on hot days? How are utility bills compared to the old system? The system may be over sized, there may be wiring issues, they may just need to make a change in thermostat settings, to name a few.

  3. #3
    Join Date
    Jan 2017
    Posts
    14
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    Thread Starter
    So many questions! :-) They did have to replace the thermostat a while back so entirely possible they didn't set up the new one correctly. Had to come out a time or two as it was to correct incorrect settings. Once the house comes up to 67, it will run for much longer periods to maintain temp, depending of course on how cold it is outside. Here in SE Virginia, temps have been fairly mild so far this winter so it's not having to work too hard. Lows just below freezing and highs 40 and up. But from an non-HVAC guy's perspective I would say it is working normally and when the installer has been out to service it during the day he runs it through the stages etc. and says all is normal. No error codes in the system's memory. Hot summer days can find it running almost continually. Utility bills are a tough call. We only owned the place a few months before we installed the new unit. Previous owner was a widow and worked all day so utility bill was probably artificially low ($150/mo according to her). We are retired so home all day most every day. That said, ours is probably around $160 on average for the year which seems reasonable to me. Higher usage but more efficient unit. Over sized? Not a clue! Think it is the same size and prior unit but can't swear. Trusted the installer to pick the right size. Wiring? They did have to replace the thermostat wire because the original one didn't have enough conductors. Outside unit is wired for 60A so I would think that is more than adequate. Wondered about the thermostat settings ourselves but installer has checked them during last visit and guess he was satisfied. Don't know what to ask him to check in the event he doesn't know all he should. He seems knowledgeable but also comments about how complicated this unit is.

    By the way, see you hail from Beatrice. Small world! I was born and raised west of you in the panhandle. Small town east of Scottsbluff. Thanks for trying to help out a former cornhusker.

  4. #4
    Join Date
    Aug 2009
    Location
    Beatrice, NE
    Posts
    7,324
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    Scottsbluff, that's on the other end of the state. My roommate from tech school is in McCook which is a lot closer than I am. Frost made a big turn around this year, hope it continues next, but hey the VB girls did good. Still not sure about Miles.

    Back to the issue at hand. There are settings in the thermostat that control the cycle. A lot of times they just get left on default so that may be something to check.

    The reason I asked about bills is wondering if back up heat was coming on when it short cycles. With that low of bill I would doubt it. Try leaving the thermostat down to see if it continues to short cycle during the day. If it does then it would be easy for them to see what it is doing.

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