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.