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  1. #1

    Trane SCUV problem

    Trane Self Contained Unit Ventilator / A.C. will turn on and run for about 10 minuites bringing the supply air temp down so low that the supply air sensor shuts the unit down completely. This wouldnt be all that bad if the unit would come back on. I have to kill power to the unit and start over. Other units in the building have gone off on S.A. low limit but come back on when the temp raises to normal. Another thing I noticed is the zone sensor on the unit seems to do nothing at all. I took an ohm reading on it like the units service literature told me to and I found no problem. Basically I don't know whether I have a zone control problem or a bad control board. Other things I ruled out are Low Pressures, Dirty Coil, Bad supply air temp sensor. The TXV seems to be non-adjustable so I cant even mess with that! Just wondering If anyone has been in this situation before and can give me a pointer before I go wasting money on any more expensive parts.

  2. #2
    Join Date
    Aug 2006
    Location
    Mixing oil and fire with a big spoon.
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    4,493
    hey, welcome to the forum.

    ya got a full model number? how is the airflow? you may need to make sure that the zone sensor is hooked up.

    good luck.
    "If you pull one more stunt like you just pulled with Tommy, you won't have to get on a plane because I will personally kick your ass from here to Korea!" - Best of the Best

  3. #3
    Join Date
    Mar 2007
    Posts
    3,124
    A full model number would be helpful but it sounds like low/no airflow without any further information.

  4. #4
    The model # is TACB0543WA0A31050 The unit has two zone sensors, one in the unit and one on the wall of the room. All the SCUV's in the building are connected to a TRANE Everyware Tracer Control system. I have no info on this tracer.

    Today I checked to make sure the unit zone control was completely hooked up and it was, however I noticed on the wire diagram a note that stated if the unit has a wall mounted zone sensor as well as one in the unit then you must remove a wire from the unit mounted zone sensor and disconnect the return air sensor. I did this and the unit now cycles normal....only when its set to 65 degrees on the unit zone sensor. Any other temperture and it locks out on S.A. low limit. Im going to replace the unit zone sensor tomorrow and see how it acts then. Like I said on the original post, other units in the building have gone off on S.A. low limit but come back on flashing a code on the LED diagnostic CR26 which means the tracer overrode the low limit alarm and allowed the unit to come back on. My unit does not do this, instead it shuts down and CR26 is steady. I have to reset manually. My company just got the maintenence contract on this place 3 weeks ago and this unit which according to workers in the building "has never worked right" is now my problem. It's 11 years old and Im the 11th service tech trying to get it to run right.

  5. #5
    Join Date
    Mar 2008
    Posts
    71
    Quote Originally Posted by RSM4LIFE View Post
    The TXV seems to be non-adjustable so I cant even mess with that!
    Thank god

  6. #6
    Join Date
    Apr 2005
    Location
    Niagara Falls,NY
    Posts
    93
    I just came across similar problem. Blower motor single speed, someone installed a transformer with a multi tap secondary winding to the motor in an attempt to reduce speed. Probably because unit was too noisey. They used the 75 volt tap( 115 volt motor nameplate) Blower was running at like half rpm that it should have been. Same symptoms--- low suction pressure, super heat,and discharge air temp. 35 deg temp drop across evap. Hope this helps u out.

  7. #7
    Join Date
    Aug 2006
    Location
    Mixing oil and fire with a big spoon.
    Posts
    4,493
    Quote Originally Posted by RSM4LIFE View Post
    ... Like I said on the original post, other units in the building have gone off on S.A. low limit but come back on flashing a code on the LED diagnostic CR26 which means the tracer overrode the low limit alarm and allowed the unit to come back on. My unit does not do this, instead it shuts down and CR26 is steady...
    perhaps the BAS is not programmed to reset this unit automatically like the others. perhaps a call to your local trane office to get a BAS tech out there to look over the system programming would be of great benefit.

    by the way, just because the other units are not manually reset, does not mean that they are not having problems! i would not recommend that the BAS system ever reset a diagnostic that would normally be a manual reset requirement!

    good luck.
    "If you pull one more stunt like you just pulled with Tommy, you won't have to get on a plane because I will personally kick your ass from here to Korea!" - Best of the Best

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