how to kill heater but run fan only on ducted heater

[rgormley]

This may be a little off topic but....

I will be running a small air con from my solar setup and I wish to use our existing ducted heating system to suck the cool air from the return intake and distribute to other rooms.

BUT I need to know how the heater can be switched off and only run the blower fans.

When we got a quote for the air con unit the installers said they can re-wire the control for the ducted heater so it only runs the blowers.

Can't really ask them how to dot it.....

So I'm asking here.

Model STADT P20

Thanks, any ideas welcome.

.....Richard

[Opera House]

Almost all furnaces have the option to run just the fan unless yours was made in the 50's.  This info should be on the furnace control.  Buying a new thermostat will give you that switch and give the color code for the connection.  Might need to run a new multicondutor wire to the furnace.  

[rgormley]

ok up in the roof space i go!

will have a look at the control box on the main unit when i get home from work

i know the thermostat only has a switch that is closed when the lever is moved from the off position, an the mercury tilt thermostat has two wires, but i presume they will just tell the main furnace to "fire" up and blow/heat.

Ok will look on the furnace......tomorrow

[Ungrounded Lightning Rod]

Furnaces may also have, in addition to a "fan on" control for ventilation, a separate "air conditioner on" input.  This provides a low-voltage output to turn on the air conditioning compressor, and may allow selection of a different fan speed for the AC, perform additional timing functions (like let the fan run on for a bit after the compressor stops), and so on.

Of course if they don't you can still use the ventilation fan-on setting to couple with an air conditioner.

If you don't have the manual for your furnace, there may be a wiring diagram inside the cover.  Or you can get the model number and consult the manufacturer.  Failing that, the terminals will typically be labeled with a letter for the color of the thermostat wire to be connected and the code is standard.

[stephent]

Look on the side of the furnace for a small switch labeled "Summer--Winter"--switch it to "Summer".

[rgormley]

Sweet!  opened the cover found a set of contacts marked "fan" measured the voltage showed 24 volts.

hooked a swtich to it and bingo! fans only!

thanks people for the advice....

now i can get that chilled air con air circulating around the house (or more so down to my computer/work room! via the heated duct tubes.

....Richard