On Monday, July 7, 2014 9:07:04 PM UTC-5, philo wrote:
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.
On Monday, July 7, 2014 10:14:57 PM UTC-5, Davej wrote:
So perhaps that was at least part of my trouble. When my furnace was instal
led they did not connect the yellow wire to the furnace control board. Perh
aps they were afraid there might be another 24V transformer somewhere and d
id 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.
On Tuesday, July 8, 2014 8:08:01 PM UTC-4, Davej wrote:
Assuming the wiring followed typical convention, yellow is for AC.
If you have AC, it has to be connected or the AC won't run. If you
don't have AC, then you don't need the yellow wire.
stat now turns off the outdoor A/C compressor and then the blower fan turns
off a few >minutes later.
It's not at all clear what's going on here, what was connected, what was
working or not working. But if this was a typical install following wire
colors, the AC would not run without the yellow wire attached to the furnac
The yellow wire is the call for cooling.
Also there could be 24V AC x-former for cooling and heating separate.
Rc and Rh terminals are usually tied together having one x-former.
Simply consult the user manual for your 'stat for typical wiring example
drawings. No buts, no ifs, just do it right. No exceptions. Blower does
not turn off right away, turn off delay is adjustable.(by jumper or dip
switch) The reason is obvious.
On Tuesday, July 8, 2014 7:46:45 AM UTC-4, Stormin Mormon wrote:
It's because the typical gas furnace can have AC added as an option.
Yellow is the control wire for AC and the furnace control board runs
both the heat and the AC, if the AC is installed. It's a minimal addition
to the control board circuitry and makes more sense than having two
different versions, one for furnaces with AC and one without.
If there is no AC, then there is no need for connecting a yellow wire.
It might still be done though, to allow for AC in the future.
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