i have an old furnasman gas furnace.
It has AC
there is a honeywell transformer screwed on to the electrical connection enclosure i suspect it was installed when the ac was installed.
I want to replace the fan motor with a 2 speed one
i want to add a switch to the furnace so i can have the fan on all the time in slow speed. then when the burner or the ac comes on it will change to high speed.
is there a relay i can install to do this or is there something else i need to do.
I think many (most? all?) furnace/AC combinations already incorporate dual speed fans. Are you sure it doesn't already have the capability you seek? You might just need an appropriate thermostat.
I believe you are correct. The heat uses the low speed and the AC the high one.
Don (e-mail link at home page bottom).
Actually mine has several speeds, not sure how many. only three can be controlled from the thermostat however. By moving wires around on the circuit board you can change which speeds are used for which events. I think the way it is set up now, if you command the fan "on" from the thermostat, it runs at a low speed, in "heat" mode it runs at a medium-high speed, and on A/C it runs at the highest speed.
I have on occasion found it useful to command the fan on even when the furnace is not running, e.g. if someone is doing a lot of cooking in the kitchen on a cold day it can be cold upstairs because the thermostat is on the first floor, keeping the air circulating not only cools the kitchen but tends to even out the temperature throughout the house.
I've also completely closed the supply dampers on the first floor, but that's primarily because of the dramatic difference in insulating properties between the first floor (block walls with brick facing) and the second floor (sticks 'n' shingles) - I do plan to have the second floor insulated but not until I'm done fixing all the wiring.
Anyway back to the topic at hand... it sounds like the OP does need a new thermostat, and probably also needs to pull a new cable between the thermostat and furnace to allow for more functions. (typical heat only scenario would only require two wires, but heat/cool/fan only would require at least four.)
nate
Hmmm, My impression is OP has a OLD furnace which does not have multi-speed fan and or elaborate electronics control board.
LOL
It must be horribly inefficient. Run of the mill new ones are 80%. I've just learned that the Carrier Infinity with the outside air duct runs at
96.6%. Efficiency can be measured with a sniffing device that measures the outtake air. I think it's time for you to upgrade.Don (e-mail link at home page bottom).
"there was no?" great!
efficiency can be measured with a "sniffing device?" that measures the outtake air? LOL
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