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  1. #1
    Join Date
    Sep 2006
    Location
    chicago
    Posts
    19

    trane ycd high limit

    having difficulties with a trane rtu that is going off on high limit. Changed gas valve because old valve could not be set at -.20 which is required. Checked airflow and it is right on, tech support says pull burner plate and check for pinholes in bottom of burner barrel. Any one ever had this problem?

  2. #2
    Join Date
    Jul 2006
    Location
    Anytown USA
    Posts
    2,060
    pull the limit and stick your temp probe where the limit is to see what the actual temp is to make sure the limit isnt opening to early.

    how did you check the air flow and find that its "right on" ?

  3. #3
    Join Date
    Aug 2006
    Location
    Wisconsin
    Posts
    1,504
    That rtu has two limits, a fan failure limit and a high limit. The fan failure has a cap tube that goes thru a copper tube at the lower right corner of the heat section. They do go bad and trip prematurely. The heat exchangers can go bad as with any rtu. I would pull the side of the unit to inspect the entire heat exchanger.
    Buy American! The job you save may be your own.

  4. #4
    Join Date
    Sep 2006
    Location
    chicago
    Posts
    19
    first thing i did was test temp inside the limit well. i was getting 225F and the limit opens at 180F. Unit is rated for 3400 CFM, using a simple formula of btu/temp riseX1.08 i came up with 3300 CFM. Also amp out motor changed filters and belts and visually inspected duct and evap coil for blockage. Pulled top of unit off but could not visually inspect bottom of burner barrell. Tech support says pull burner plate ,and inspect from inside out. Tech support says this unit is known to get pin holes and radiate heat directly onto cap tube. Just curious if any trane guys have dealt with this

  5. #5
    Join Date
    Aug 2002
    Location
    Southern NJ
    Posts
    962
    I like to verify airflow (cfm's) from the space it serves, using a flow hood. I've seen insulation inside the ductwork drop and create restrictions that cause the unit to trip. I've also seen it happen on the return duct.

    Unit rated at 3400 cfm's and your getting 3300 cfm's.....is there any duct work on this unit? Once you put a duct system on this unit the cfm's will drop thru 90's and branch dampers. That's why I like to have real time data.

    Check your static pressure in the supply plenum and see if you have a airflow issue.

    As the other Guy's stated sensors do fail.....
    I love to Cook...HVAC is a hobby that pays the bills!

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