Hey all you AC types got a weird issue

[rwe2156]

Note: what I'm going to describe has happened before the tech replaced the thermostat which seemed to solve the problem but it happened again yesterday.

The issue before was the air handler would not turn off when reaching set point.  If you switch fan from auto to on and back to auto it shut off and cycled normally after that.  Might go a few hours, or a few days and do it again.  Finally one time, the only way I could get the air handler fan to turn off was throw the breaker.

When this is happening the outside unit it not running.

After 3 or 4 months of normal operation, it did it again last night.

The only way I could get the fan to turn off is throw the breaker.  I left it off overnight, when I turned the breaker on this morning, the fan started running. (Thermostat is not calling for cooling at this point).

He's coming out tomorrow but said he's not sure what's going on he's thinking its the controller board on the air handler.

[blackhat]

It could be an intermittent short in the control wiring. If there's 24v between G and C when the stat is off I would suspect that's the case.

[Roly]

Note: what I'm going to describe has happened before the tech replaced the thermostat which seemed to solve the problem but it happened again yesterday.

The issue before was the air handler would not turn off when reaching set point.  If you switch fan from auto to on and back to auto it shut off and cycled normally after that.  Might go a few hours, or a few days and do it again.  Finally one time, the only way I could get the air handler fan to turn off was throw the breaker.

When this is happening the outside unit it not running.

After 3 or 4 months of normal operation, it did it again last night.

The only way I could get the fan to turn off is throw the breaker.  I left it off overnight, when I turned the breaker on this morning, the fan started running. (Thermostat is not calling for cooling at this point).

He's coming out tomorrow but said he's not sure what's going on he's thinking its the controller board on the air handler.

I will guess the fan relay is sticking.   If it is still running when serviceman gets there he can check if relay is energized or not.   Roly

[TDKPE]

I can hear the relay for the fan clicking in my thermostat, so under manual control I can hear it close and open.  When you turn the fan on manually, can you hear the relay clicking?  And more importantly, can you hear it clicking when it opens to turn the fan off?

[Roly]

I can hear the relay for the fan clicking in my thermostat, so under manual control I can hear it close and open.  When you turn the fan on manually, can you hear the relay clicking?  And more importantly, can you hear it clicking when it opens to turn the fan off?

The relay is in your thermostat ?   Mine is in the furnace.   Roly

[blackhat]

You have one each. Just a matter of scale.

[TDKPE]

Yeah, I meant the little one in the thermostat.  I can hear mine clicking on and off for heat and A/C and the fan when selected manually.

If the OP's clicks to release the fan but the fan doesn't turn off (in A/C mode, at least - my furnace has a blower thermostatic on/off delay), it would at least narrow it down to wiring or air handler control board or relay.

[Roly]

Yeah, I meant the little one in the thermostat.  I can hear mine clicking on and off for heat and A/C and the fan when selected manually.

If the OP's clicks to release the fan but the fan doesn't turn off (in A/C mode, at least - my furnace has a blower thermostatic on/off delay), it would at least narrow it down to wiring or air handler control board or relay.

Mine is old school, relays and sequencers, no electronics.   Easy to troubleshoot.  Roly

[Pirate]

Fan relay n the air handler, is vote.

[brianwelch]

Fan relay n the air handler, is vote.

What Pirate said ^