Ah,
I think I know what is happening. A lot of Candadain Geothermal units are a combination of geothermal for 80% to 95% of the heat / cooling, and then in extreme whether conditions have a back up heater of some sort to keep your unit at a certain temperature. this could be a heating coil or whatever.
I don't know much about A/C but there may be electric backup A/C as well.
Refrigerant or fluid like glycol or water, perhaps even freon? might be normal in the unit, if it is not an air to air type exchanger. (e.g., ground or water is used as the heat sink / heat gain source).
Our whole house fan for our traditional natural gas furnance (that runs when the furnace runs, or when we have it set to fan only to circulate air) takes $40-$60 per month in electric bills, at 10cent/KWH, for a 2 storey home. If you do not have a variable rate fan, then yours is all on or all off (DC fan), and likely drawing this much even if no supplemental heating is involved.
How is the electric for the main geothermal unit in the basement paid / metered? Separate meter landlord pays and you just run your unit?
Can you get the make and model of the fan / equipment in your unit? You should be able to find out if you have a top up heater / chiller in there, and could cut costs drastically by letting temps fall when it is cold outside, and the basement unit is only putting out 15'C heat..
I would research what you can do to reduce these costs -- like turning it way down, fan is not running continously, etc. If you can not reduce the costs, just start letting your landlord know that you will be trying to find a new place, and why. Maybe he will help you end your lease sooner if you talk about the money bind and desire to keep up payments but will have trouble eventually...
Next time, I guess you ask to see typical monthly electrical bill before signing lease... People do that when buying houses, so I don't see why renting should be different.