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Robi.1014 05-24-2012 09:43 AM

Using AC, fan never turns off
Hi All,

My Trane system (with 19i compressor outside) has a T803A thermostat. I have the FAN set to AUTO. When running the AC and the desired room temperature is reached, the fan continues to blow....never turning off...blowing at 100% speed.

If I raise the SET TO temperature up one degree (or more), the thermostat's internal relay can be heard to click, and within seconds, the fan stops running. But subsequently, when the room temp increases to the new SET TO temperature, the AC comes on, the fan blows, the room cools down, etc. But again, when the 19i compressor shuts down, the blower/fan continuous blowing mode at 100%...never turning off. This condition is similar to setting the fan "ON" all the time....and clearly not what I want. Thoughts?

clocert 05-24-2012 10:17 AM

Either T-stat problem or Control module for your blower.

hvactech126 05-24-2012 09:40 PM

just because the indoor temp matches the setpoint on the thermostat does not mean that the a/c should shut off. Todays thermostats have close tolerances. If you set it at 70F it may not turn on until 70.5 and may not shut off until 69.5 while all the time showing 70 on the thermostat. The blower should slow down. The 19i is a 2 stage system and contains 2 compressors are you sure it has not dropped down to first stage when you think it has shut off? It could be that you have 1st stage problems with your unit. It could be that it is not wired properly. Is this a new system?

Robi.1014 05-24-2012 10:18 PM

Understand your thoughts on 70.5 & 69.5 showing 70....and the fact that the 19i is a two-stage unit. But you probably agree that when the fan is set to AUTO, it will turn off once in a while. Mine does not. If left alone, the fan will run 7/24. Buttttttttttttt..... Under two conditions the fan will perform the on/off that it should when set to AUTO: (1) when I raise, the temp 1 (or more) degrees (like I wrote initially), and (2) if I pull the thermostat off the wall and then re-insert it. In both cases, the fan will perform an AUTO on/off once or twice, then revert back to never turning off.

I'm thinking it's the thermostat. Is there a reset (to factory) button on that thing?

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