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lettersoup 11-10-2011 08:06 PM

separate switch for blower in HVAC system
How do I rewire my forced air HVAC to install a switch, separate from the one on the thermostat, to activate the blower? I want this separate switch on the second floor so I don't need to go downstairs to the lower lever, where the thermostat is, if I want to turn on the blower.
I thought it was just a matter of adding my switch hooked to the G (which I though controls the blower) and R (24 v hot) terminals, in parallel with the thermostat. It worked fine if the thermostat (Honeywell TH4110D1007-0645) is not pushed into its base plate but once I install the Thermostat back, when I flip my switch on, the AC starts along with the blower, even though I am not connecting the Y wire (which I thought controls the AC) at all with my separate switch. It seems as if the thermostat is causing the connection whether it is in OFF, in HEAT or in COOL, regardless of the temperature settings.

hvactech126 11-10-2011 10:53 PM

you will need to add an isolation relay.

lettersoup 11-11-2011 09:04 AM

Thanks. The devil is in the details... Will I need to isolate all four connections from the thermostat or I just the Y (and perhaps even the Y and W wires) with a DPDT 24v signal relay?

gregzoll 11-11-2011 10:13 AM

Why not just swap out the thermostat with one you can control via remote. Either through wifi, or a remote. There are various ones out there, that would be better, than attempting to rewire, and then screw up the control board.

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