If the furnace or A/C unit is not working but the Fan is still on, this is generally an issue caused by low batteries in the thermostat. Batteries are the responsibilities of the tenants (per the lease). Please see the video below for general help on replacing the thermostat batteries.
Dirty Air Filters can also be an issue if the HVAC is running inefficiently. Changing those out will clear the air flow and allow the systems to function properly. Per the Lease, tenant's are responsible for switching these out. they can usually be purchased at Home Depot or any hardware store for less than $10 and only need to be replaced every 2-3 months.
To hard reset the HVAC system, you can find a switch on the outside or near the furnace like the one pictured below. Make sure the switch is in the "on" position. Switch it off, wait 30 seconds, and flip it back on.