anybody remember that post about the furnace?

[sak4kat]

Some of you responded with some helpful information bout' our furnace.  So I have one more question to add to that.  If I have my thermostat set on 73...auto...than the fan and furnace run simultaneously...when the thermostat reaches 73 should the fan turn off?  Mine just runs and blows cold air.  Temps drop. Than the igniter tries to turn on but can't seem to get lit to stay on?  So I turn the furnace off at it's main power switch.  I leave it be till this place get's so cold I can't stand it any more.  Than when I turn the furnace back on...I have to adjust the thermostat and repeat.  What do you think the problem is?  My landlord keeps telling me it needs to be cleaned?  I don't know what that means.