Mr. Mark wrote:

it's chewing up a lot of electricity (1000 kw/h per month).
should it be running constantly? if not, how can i turn it off? and
should it be using this much electricity?


The fan relay switch contacts may be stuck closed --or on. First,
disconnect the power.
You could tap it lightly with the insulated head of a screw driver.
Connect power, still run?
Don't blame me if you brake it! Welded switch contact points won't
release with tapping.
Also, tap the furnace near the fan/limit switch.
If either stops the blower, --set the fan switch to a higher shut-off
temperature.
If a defective switch, disconnect the power source, and replace the
defective component.
Don't electrocute yourself!
If you don't know where those switches are, call a tech. -Darrell

--
Air Conditioning System Sizing for Optimal Efficiency -
http://www.udarrell.com/airconditioning-sizing.html