I have a 2010 avenger. I don't think its the

heater radiator or some hose damage

It sounds like you may have a slight heater core leak and when you turn on your air, it's simply "stirring up" the smell. I've never seen this issue ina Focus but i have in a '97 Bonneville. The heater core is located behind the dash and requires complete dash removal to locate. It's a rough job to tackle alone. A lot of shops can run a "leak test" where they run a pink dye through your A/C system and see if it leaks anywhere. You may simply have a dry-rotted hose or bad seal. But my bet is the heater core, as thats the only place antifreeze enters the interior of a vehicle. Try smelling up under the dash on the passenger side and see if the smell exists there. If so, it's a heater core leak. Hope this helped!

How to Replace Your Heater Core:
First remove all the water from your system by draining the radiator, it's best to do it this way so you can add new coolant and keep the mess to a minimum, after your water is drained, go ahead and remove the heater core feed lines.
1.Remove top of dash pad, do this by removing several screws located under the foward lip of the pad, don't forget the screws in the defroster vent holes!
2.Remove the lower trim panel from the underside passenger side dash ( if there is one there)
3.Look under the dash on the passenger side and you will see the plastic box in which houses the heater core, remove all the screws that surround this box, there will be one screw on the top that will be very difficult to get at, this is why you have removed the top of the dash so you can get at it with two hands,if you need to see this screw get outside of the car and look down at the dash from the passenger side and then your going to have to depend on feeling with your hands.
4.At this point you should have the plastic box off and now your looking directly at the heater core, the core is held in place by a steel clamp fastened with screws, remove these screws, and remove the clamp.
5.Now it's time to remove the heater core , get some plastic sheeting and lay it around the passenger foot well because there going to be some water in the core yet, pull it out gently, you might have to wiggle and gently pull, take your time, it should come out fairly easy.
6.Once you have the old core out, it's time to install the new one, I can't tell you how important it is at this point to be very patient when installing the new core, you may have to slightly bend the new core tubes to get them through the firewall, you may end up taking it out a couple of times BE CAREFULL!!!!!!
7.Once you have sucessfully got the core in place, install the core clamp, then re-assemble.
Make sure that after you have installed everything and you fill your system with water, slide your heat temp control to full heat the check everything for leaks!

That's the heater core leaking into the heater box under the dash.

The evaporator is located in the heater box, it is the AC's equivalent of a heater core. Water is a NORMAL by product of refrigeration, and the clear water must leak out to the ground.

Typically if your leaking coolant inside the car, it indicates your heater core is split and leaking. Replacing the heater core is quite the job. It requires removal of the dash board and heater box. i replaced one in a 97 Cirrus at work last week and it was a 6 hour job. If your not mechanically inclined i would definitley recomend phoneing around for quotes to local auto repair shops and getting it done profesionally.

Replace heater core, usually under dash passenger side. you may get lucky and find yours removes under hood on passenger side .you will have to look Im not farmillier with your truck. if it can be taken out under the hood its not a bad job.under the dash is a lot tougher.

Your heater core is leaking, and when it does, it drains into the foot well passenger side. Best case would be a hose that is leaking, worst case is the core itself. Replacing the core is a big job.

If leaking coolant under dash on passenger side floor broad it's your heater core. Call's for 2.8 labor flat time to remove heater core, in some case's you'll have to recover, evacuate and recharge your A/C system to remove your heater core.Sit under dash on passenger side.

Your heater core needs to be replaced. It's located on the passenger side , under the dash. The heater core is like a small radiator. Coolant from the engine is circulated through it, and that is what provides heat in the car. The heater core is leaking, causing the 'vapor' through the vents, and leaking on the carpet on the passenger side. Heater cores are a pain to remove and replace, it's quite a labor intensive job.