trane tracker sensor

[comer]

i am having problems with a sensor on a trane system. the initial call is that unit is freezing up. after several attempts to locate problem i realized the temp was reading 108f and it was only like 76f. i realize it works off resistance and was told to see if problem was shorted and put bulb sensor straight on board. the temp was reading accuratly. ran a new tstat wire to return and hooked up sensor. came back and temp was way off again. friend told me i might have used too large of a wire because it works off resistance. ran smaller wire no help now if i put bulb to board still reading is off. is board, bulb, or is something else bad. would appreciate some help thanks.

[rick4670]

what is this sensor used for, outside air temp? Just wondering how you know it was reading 108.

[heatingman]

All trane sensors are rated at 10,000 ohms @ 77 deg f.

1 were you using the same sensor?
2 If this is for a indoor temp sensor, trane like to use averaging sensors. Meaning more than one sensor in a series, to average more than one sensor together for one data point.
If there is only One sensor, then there should be one thermistor under the cover. If there are 2 sensors, then they should be wired in series, and there needs to be 2 thermistors under each cover.

Its not likely a wiring size issue, may be a really bad conncetion, but I'm guessing there averaging sensors, and one or more of the thermistors is bad causing bad readings.

[heatingman]

what is this sensor used for, outside air temp? Just wondering how you know it was reading 108.

The LCD on the tracker panel Told him. Which tells me indoor temp. If there is a aux OA temp sensor, it would not control the unit, just a convence for ems geeks. The OA sensor on the unit control fan staging for low ambient condition.

[Tech Rob]

Are you using shielded cable? I'd imagine it's one of two things... A malfunctioning sensor, or electromagnetic interference from something close to the wire or sensor itself.

Had phase problems at a site once that made sensors do all sorts of crazy stuff. A signal coming from a controller or module is only as good as the power supplied to it.