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  1. #1

    Carrier 95 Model 59TP5A Gas Furnace - Quick Cycling

    Two months ago, replaced our 23 year old Carrier gas furnace with a Carrier 95 Model 59TP5A two-stage ecm furnace. The system will cycle approx. 5-6 mins on and approx. 7-10 mins off. We notice this cycling more in the evening/night then the day. Probably because the temp drop during the night. Our old furnace never did this quick cycling....at least it seems quick to us compared to our old system. Is this the norm for a 2-stage furnace? We are using a single stage t-stat. So the 1st and 2nd stages are controlled from the furnace board and not the t-stat.

    Thanks for the feedback.

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,875
    Should use a 2 stage stat. But that probably isn't the cause of the short cycling. The CPH of the thermostat may be set to high. Is the new furnace the same BTI input as the old, and was the old furnace a 80% furnace.
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  3. #3
    Don't know the old BTU but it was a 90% Carrier. The btus on the new unit range from 66K to 100K for a 2400 sq ft home (excluding basement - which does have two heat ducts and a return...semi finished).

    What is CPH of the t-stat? And is the problem that the furnace control board is running the furnace on a timed basis as opposed to the t-stat running the furnace on a temperature basis?

    I've posted earlier about running a 2-stage furnace on a 1-stage tstat and feedback was it's ok to do so. The contractor said the same thing. Difference is the control board on the furnace runs the system not the tstat.

    We know Carrier has a good reputation, but we wish we had our old furnace back....simple, straightforward, no microprocessor making "intelligent" decisions about running times, efficiency, burner adjustments, etc. I'm sure Carrier would be happier too but the Government probably has set certain energy efficiency standards that must be met. Sigh.

  4. #4
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,875
    CPH is cycles per hour.

    If the board timer is set to go to second stage after 5 minutes. Its not doing you much good having a 2 stage.
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  5. #5
    Join Date
    Jul 2005
    Posts
    5,491
    Quote Originally Posted by beenthere View Post
    CPH is cycles per hour.

    If the board timer is set to go to second stage after 5 minutes. Its not doing you much good having a 2 stage.
    The CPU uses adaptive algorithms, allowing up to 16 minutes runtime in low heat.

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