Foul odor out of vents when I turn heater on

Are you loosing radiator fluid. sometimes the heater core will rupture and you will smell burn odor. also check for strange rubbing sounds or screeching coming from the blower fan motor. or engine exhaust manifolds are hot when car is on, make sure nothing is leaning on them which will cause a burn odor. Any odor coming from outside will find it's way inside through the fresh air vents.

sounds like a mouse nest in hvac system, no smell because when using ac it doesn't use outside air, probably a nest on the screen at the hvac air intake or if you have a a cabin air filter check in there. many times rodents make nests have babies and then the car moves and they cannot feed the babies and so they die and rot smell comes into car. usually it is not hard to access because there should be a screen between the outside and inside under the cowl cover, if no screen and the little buggers vot into your hvac duct system this could be a much bigger problem entailing removal of dash completely. most likely this isn't the case, good luck

i use a rubber hose to my ear
then move it about the dash, find the clicker.
then photo it and ask for what it is here, click add photo.
or with same photo, look in the fsm
or
alldata.com

If it's a nauseating sweet smell, it means your heater core is leaking into the air box. It will have to be replaced.

Sounds like your off timing. Make sure that your timing gears are set on the marks properly. The foul odor your smelling may be because your car is running rich.

Dead field mouse or cat? Usually caused by build of smoking and other odors that stick to the condensation created by the a/c and eventually becomes kind of a permanent smell in the vents.

Check for loss of coolant also. If you can see/smell oily deposits on windshield, it's unlikely it's from the a/c system as there is relatively little lubricant there. More likely your heater core is leaking and allowing coolant to be blown up onto the windshield. There will also be a distinctive odor with this.

Check for a seized pulley

With the belt removed turn each pulley by hand, they should all move smoothly without barely noticeable play. I suspect that you may find the idler pulley is either locked in position or locks up occasionally. When turning the pulleys try putting some up or down pressure on them.

The smell you are detecting is most likely the smell of the burned belt. They do tend to give off a smell that keep on giving long after the bet is gone.

If you run your Air cond on recirculate always try using an air sanitizer in your return vent. Or switch your A/C to outside air flow for for half an hour and raise the rear of your sunroof panel to vent the stale air do this till the smell dissipates and then close he sunroof and reset the A/C to recirculate if desired.

1st, the fuse location is marked, what is the 20 Amp fuse for? 2nd, did the smoke have a nauseating sweet smell to it? If it smells like described it is the heater core leaking, coolant steam looks like smoke.