On Monday, July 7, 2014 10:14:57 PM UTC-5, Davej wrote:
On Monday, July 7, 2014 9:07:04 PM UTC-5, philo* wrote:
On 07/07/2014 08:55 PM, Davej wrote:

So why does a gas furnace control board have a
contact for the yellow wire? It makes no sense to me.

What makes no sense is your vague question

I think it is because while the green wire or the yellow
wire will turn the blower fan on -- the yellow wire will
also cause the blower fan to remain on for a minute or
so after the compressor turns off.


So perhaps that was at least part of my trouble. When my furnace was installed they did not connect the yellow wire to the furnace control board. Perhaps they were afraid there might be another 24V transformer somewhere and did not want to mess with it. With the yellow wire connected the thermostat now turns off the outdoor A/C compressor and then the blower fan turns off a few minutes later.