I have a air conditioner to cool a building and a hot water system to heat it.
Each have their own air mover (fan). They are being controlled by one conventional thermostat. The air conditioner it wired correctly except that the FAN wire isn't connected to the air conditioner air mover. FAN is connected to the hot water air mover. So..the heat has to be turned on and off manually. This is a very awkward situation. Anyone have any ideas on the best way to remedy this situation?

 

Get a fancier more functional digital thermostat.

There are many now that will do all that and more for less than $100.

 

Why can't you just connect the AC control signal to also control the AC fan and the heat control signal to also control the heat fan?

 

This doesn't make sense: The fan command from the thermostat is wired to the heat system, making the heater fan fully automatic, therefore the heat has to be turned on and off manually.

The air conditioner system is wired correctly except it isn't wired correctly so the fan doesn't come on.

Want to try again?

I think I have it. Wire the green fan command to the a/c air handler and use the white command wire to turn on the fan relay in the heater.

 

I think I have it. Wire the green fan command to the a/c air handler and use the white command wire to turn on the fan relay in the heater.

That's the way to do it.

Or vice versa, use the yellow to pull in fan relay on cooling.

Leave which ever system connected to green that you want manual fan control.

What makes this system odd is that most heating systems use a type of thermodisc heat sensor to turn fan on. This prevents blowing cold air and keeps fan on until residual heat is removed.

 

yes. I'm thinking, where's the stack switch (or similar)? The heater should be controlling its own fan.

 

If it uses hot water for heating then perhaps the radiator is hot all the time and only the fan is turned on and off to control the temperature. In that case there wouldn't be a thermodisc switch to control the fan.

 

In that case conventional wiring.


W to heat air mover
G to AC fan control
Y to AC contactor

Red from both transformers
Yes you can! As long as nothings grounded.