Gas and Oil Home Heating Furnaces - the dreaded blower always on saga

i have a ruud downflow fuel oil furnace, model no.(uonc-084qbea) that the blower stays on constantly, the burner works properly, the only way to turn off the blower is to turn off the switch by the furnace, i have had one person say it is a timer, another say it is a low voltage relay and another says it is controlled by a coil of some sort that contracts and expands with the heat and cooling that activates the blower and shuts it off, could someone give me a clue on what to look for, i have already shelled out too much money to a professional only to have the same thing still happening

If it's a timer it's intigrated into a circuit board, it could either be a relay or fan limit.

Can you remove the front cover of the furnace and explain what other controls are in there besides the burner.

there are 2 compartments, the bottom is mainly relays for which i have already had replaced, 1 of them the thermostat hooks into but the top compartment where the blower is there is a black box with 2 heavy gauge red wires with female connectors on them, they plug into the black box, the box is approx. 2 in.wide by 3 in. long by 1 1/2 in. tall with 5 wires total running to it,all plugging in to it, it is mounted to a box kinda resembling a receptacle box, it has wires running from the blower to it and wires coming out of it and leading to the bottom to the other relays, could the black box be what i should be looking at? the furnace is about 6 or 7 yrs. old and i don't believe i see any circuit boards of any kind on it, thanks for the help

How old is this furnace can you have a fan limit control there pull the cover and see what you have.


Ed ;)

my above post has the age of the furnace, anyway i pulled that black box i spoke of earlier off of the furnace and it has a little dial with a screwdriver slot on it, on the lowest setting side it has 150 sec. and the highest setting it has 200 sec. i think this is the problem, i pulled a wire from it and turned on the switch and the blower doesn't work, then i hooked it back up and it stayed on non stop again, i hope this is it, the mornings are getting colder

That very well could be it. After the burner gets a call for heat the timer times out and turns on the blower.

Are you able to decipher the schematic.

i talked to a ruud dealer and am supposed to get a timer friday, i also found a board or something that has 2 wires that plug to it that bolts to the side of the plenum and it has a cover that slides over it and one side had burn marks on it like it shorted out, gonna check that out also, i am able to cipher out the schematics, thanks for the responses, it is greatly appreciated