Hi,

I would like to add a switch to my furnace so I can turn the fan/blower on and circulate air in our house in the summer.

If you look at picture 'B' below you can see I wire sticking out from the 'R' connection - I tried to jump the 'R' connection with the 'GH' but it did not work after I put all the covers back on and flicked the power switch.

(The R to GH is something I read on another forum)

I'm hoping someone can look at the furnace setup in the pictures below and tell me how to wire this to turn the fan on all the time (with no heat).

Thanks...

-Chris

http://thinkbigidea.com/comp.jpg

Check your thermostat, it should have AC-Off-Heat and the fan switch should be Auto-On. Switch H/AC to Off and move the fan to On, should run. In the summer, I turn the fan to on and let the AC cycle, uses more alectricity but maintains a more evenly cooled house.

Thanks but I already tried that. It seems the thermostat does not control the blower, just the heat (no A/C). When the furnace heats up the blower kicks on. I need to manually wire a switch to turn on the fan without heat.

Tell you what I would do:

I am ASSUMING COM is L2. If this is wrong, poof. Meaning L2 is neutral. I'm also ASSUMING LO and L1 get connected together when the heater runs. You have to VERIFY.

A connection between L1 and LO should run the blower at the heating speed.

Thus a 24 VAC coil relay between thermostat common and G will give you a contact closure when FAN is selected.

If these contacts went across LO and L1, the blower will be overridden at the heating speed.

This isn't exactly what's supposed to happen. What's supposed to happen is:

In heat the furnace is supposed to control the fan at a low speed.
In cool, the thermostat controls the fan and at a higher speed.

This modification doesn't give you that.

I'll have to think harder how to get a higher speed for cool.

You could use an item like this.

Use the new fan center as a pass through for the heat blower wires since it is always activated. (just make a loop from the old wiring control fan blower terminal to the fan center then right back to the old wiring control blower terminal. (Use the RED/ RED N.C. terminals for this purpose.This will allow the furnace to operate as it always has. The pick up a constant on 120 volt power source and feed it to one of the black relay terminals on the new fan center and take a wire from the other treminal on the new fan center back to the motor high speed wire/terminal. Use the Black/Black N.C. terminals for this purpose. I believe your diagram is marked number 1 for the high speed motor terminal. NOTE: You can pick other motor speeds but since no A/C is involved I figure the high speed terminal 1 would blow the most air around.

You will have to pick up an always on 120 volt hot leg and neutral to power the 24 volt supply in the new fan center. (Not difficult since those power sources are righ there on the old circuit board.) Shown as Black wire and White wire on diagram.

Last is attach a switch to terminals R and G on the new fan center. When you flip the switch the relay in the fan center will activate and the blower will come on at high speed and run all the time all the while the red low speed wire for heat will stay out of the circuit.

This has somewhat of a fail safe since if the heat does come on the fan will eighter be in the old mode (new fan center switch off) OR it will be in the high speed fan mode (New fan center switch turned on).

I hope this will work out for you.

Nice!

If you add a small 24VAC relay to HVAC's response, you can activate by the thermostat.

Connect Normally open contacts to R and G in HVAC1000's description.

Connect one side of the coil to the old termostat C and the other side to thermostat G.

Bingo!