Do I need to replace my thermostat in the car?

I would suspect a Thermostat. It either stays open or shut. It is keeps open it never gets that warm and cold air is always blowing. Although, if it is stuck close it will overheat. I would replace it.

this would probably be due to the coolant has not been bled probley which is a comman occurrence when you get some one who does not know what there doing when refilling the antifreeze. There should be a bleed valve on the cooling lines under the hood in some cases 2 here is a link that should help you out. http://www.ehow.com/how_7675042_bleed-cooling-system-audi-18t.html . Alot of people don't realize the anti freeze cooling system in an audi is a closed pressurized cooling system and the reason you get the thermostat going up and down is the air pockets going threw your system are stuck in certain places and randomly the coolant gets threw those locations to spike your sensors. As for the heating system it will only work when your foot is pretty much half way to the floor due to the air bubbles in it as well. If you had AUDI do this work take it back and ask them to bleed your system properly and complain about them not bleeding the system properly which caused you more issues. you can do the same at where ever else you had it done but it would be best to take it to a vw or audi dealership to get it done, since they can do it properly

I have a 2005 a4 Audi Quattto that was given to me it over heat when trying to put coola t in the reserve tank had a crack in it now thats replaced its another spot where the coolant seems to be clogged or a house something is missing

is there any coolant flow? if there is zero heat coming out of the heater then you likely have a blocked or broken water pump. your going to need a flush to find out exactly whats going on here.