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  1. #1
    Join Date
    Jun 2003
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    Chicago, IL
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    Carrier RTU meltdown

    I recently cooling checkups on 5 carrier RTUs.

    I opened one to find a shredded fan belt and all the wiring in the blower compartment completely melted.

    apparently the belt broke during the heating season and the limit failed to trip. the unit ran until the wiring shorted out. Both the 24v fuse was blown and the 50A breaker tripped.

    I ended up replacing the limits on all 5 units. The units were 4 years old but this was the first season they had been used. The building had sat vacant for 3 years and there was signs of significant moisture buildup inside the units.

    Anyone seen a limit fail closed before? I never have.

  2. #2
    Join Date
    Jun 2003
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    Chicago, IL
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    Here's some pics
    Attached Images Attached Images   

  3. #3
    Join Date
    Apr 2012
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    Paper Street Soap Company
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    2,304
    Quote Originally Posted by craig1 View Post
    Here's some pics
    Thats strange .

    Electric heaters have limits plus the fan limit on the fan housing.

    So both would have to fail closed for that to happen.

  4. #4
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    Apr 2012
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    Ok took a closer look it looks like those wires melted from excessive amp draw not heat.

    Not all are melted.

  5. #5
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    Jun 2003
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    Chicago, IL
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    Quote Originally Posted by commtech77 View Post
    Thats strange .

    Electric heaters have limits plus the fan limit on the fan housing.

    So both would have to fail closed for that to happen.
    This is a 200,000 BTU gas fired unit

  6. #6
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    Jun 2003
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    Quote Originally Posted by commtech77 View Post
    Ok took a closer look it looks like those wires melted from excessive amp draw not heat.

    Not all are melted.
    most of the wires in the first pic are for an economizer accessory that is not installed. The wires just hang there, they are not connected to anything.

  7. #7
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    Apr 2012
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    ahhh I see. You mentioned a 50 amp breaker trip on a RTU and I assumed electric heat. I havent run into a gas pac RTU thats done that .

  8. #8
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    Apr 2012
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    Quote Originally Posted by craig1 View Post
    most of the wires in the first pic are for an economizer accessory that is not installed. The wires just hang there, they are not connected to anything.
    Its hard to tell from the pics whats what.

  9. #9
    Join Date
    Feb 2006
    Location
    Atlanta,GA.
    Posts
    891
    i have seen that on carrier units before. just excessive heat from heat exchanger not having air flow and it gets hot in the fan compartment.limit is probably not failed closed if you check it .I think it is a bad location but then im not an engineer, i would rather see it on the fan housing up high where the heat is

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