Trane Model # 2TWR3018A1000AA

[tinkertech]

 This Trane problem doesn"t make sense to me,so I need some help. At work, another tech said the compressor on this unit wasn't working and that the problem was the ambient air sensor. He arrived at this because there was a flashing LED on the defrost board that gave a code (2 flashes a second) and the sensor was mentioned as one of the possible causes.

 My thinking was that the ambient sensor worked in conjunction with the coil sensor to calculate the "delta T" and signal the system to go into defrost. I couldn't see how it had anything to do with the compressor not working. I turned system back on without the sensor in place and it ran fine until the next morning when the compressor was found not to be running again. I talked to two Trane support techs via phone and they said that the sensor had nothing to do with the compressor not working at times. Put a new sensor on and system has run now for a day and a half with no apparent problems. Can anyone explain how this sensor can cause this or do I have another problem that will show up again?

[ACtechGUY]

My guess (without knowing what the other possible reasons you could get a code 2) would be that the unit runs fine until time for defrost. The control then sees that the ambient air thermistor is not in range so it ignores the sensor and uses a default setting...... UNIT DEFROSTS. But what if the sensor is still out of range the next time? well it ignores it again. Well defrost #3 comes along and the unit locks out . Many controls will ignore a problem for 3 trys before they will go into a lockout mode. Also to explain why you may not instantly got an alarm code I can tell you that many electronics don't "LOOK" at specific componets until they are needed. Example: TIME FOR DEFROST( based on time setting) 1: LOOK AT COIL THERMISTOR 2: NOW LOOK AT AMBIENT AIR THERMISTOR ...NOW GO INTO DEFROST MODE.