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lightsycle · Jul 8, 2007, 07:47 PM

Ok Guys,

I found the thread about the switch for fan only by jumping the G to the R with a toggle switch. It worked. The fan comes on to circulate the air, at high speed. When the heat comes on it uses another speed which is a little slower. I know this because when I turn on my switch I get massive air movement, and a noise that can only be described as bad exhaust sputtering noise. I have a white roberts thermostat for heat and air, and a coleman GM8S gas furnace 40MBU in 32 out. I want to have the fan running either on the toggle switch or the thermostat to use the same speed that it uses when it is heating. On the unit end of the thermostat wires (2 only BTW, red and white) on the circuit board the red wire is on the R and the white is on the W, HA! On the thermostat itself I have red to B and white to W. RC and RH are jumped. Is there a way to have to thermostat activate the fan only w/o heat, or have my installed toggle switch use the low speed? the purpose is to circulate air w/o the horrible annoying noise. Unit has Y1,Y/Y2,G,C unused, and thermostat has G, O, and A unused. Y goes to the back side of the cool-off-heat switch, I think. I can include pic of both if it would help. There are jumpers on the circuit board that say fan speed - lo cool pins have been cut off, next is heat and hi cool.

Thanks

acetc · Jul 8, 2007, 08:35 PM

Can you provide more information? Number of wires to thermostat?Do you have A/C? How many wires and what color to the A/C unit? It sounds like it is not wired correctly, because the red wire should be connected to the rc-rh terminal at the thermostat, the "B" terminal is made constantly to "R" terminal when stat is turned to heat on the subbase.If it were wired correctly and the "G" to "R" jumper you installed would also bring on the A/C by backfeeding through the thermostat when in the auto fan mode. What you want to do is possible but you need to know what you are doing, suggest you hire a A/C contractor. I would like to help you further but if it is not correctly you could have some big problems. Mike

lightsycle · Jul 8, 2007, 08:43 PM

It is a furnace only unit, there are only two wires running from it to the thermostat-red and white. The thermostat is being used as an on/of switch for the heat and fan as one unit, not as individual units. Heat is working fine, but I want to use it as an air circulator.

labman · Jul 8, 2007, 09:14 PM

If you moved the jumper for the heat to the hi cool, it should work. The heat wouldn't work until you moved it back. You could also try soldering new pins to the lo cool and connecting the jumpers.

lightsycle · Jul 9, 2007, 07:36 AM

But there are no jumpers crossed. There are several other jumpers also. I am not home at present.

What about if I just hook up all the wires from the frunace to the thermostat? Wire by letters, everything except for the r-rh is just straight conect right? Will it work that way to have the unit set to off and the fan on, as opposed to auto, the fan should run right?

Thermostat
http://www.acsuperstore.com/specs/wh...w_444_inst.pdf

Furnace- closest match is the gms8 40-32 MbH model.
Coleman Heating and Air Conditioning: Gas Furnaces

I will include exact model # and pix of circuit board in unit later this evening.

acetc · Jul 9, 2007, 10:21 AM

The fan motor is brought on in low speed through the fan switch in the heating mode (as the furnace heats up the fan switch is set to bring on the fan motor as temperature rises and shuts it off when temperature drops) This is the red or red tagged motor wire. The toggle switch is wired to the fan relay which engages the high speed motor lead (black) This relay will have to be rewired to engage the low speed (red) lead to the motor and the high speed lead discontinued and taped off. Remember to disconnect power to furnace before attempting to change any wire connections. If you provide power to high and low speed at the same time you will burn the motor up. Mike