Vapors coming through the vent w/AC & heater on - 96 VW Golf

More than likely heater core leak, I assume you are losing coolant. I've changed a couple heater core in my life but nothing like changing the one in the video. I saw 3 videos, and all said you have to pull the dash.

How VW Parts Fail ~ Heater Cores - YouTube

VW Heater Core Replacement - 1993-1998 VW Jetta and Golf - YouTube

egr tube is broken check that if it fumes from the tube and replace the tube

Ford are aware of this and should hold there hands up in shame .
thay say it's the catalytic converter causing all these problems . Sorry I can't tell you any more has thay are keeping tight lip about it good luck and don't give in ps tell ford your going to seek legal advice on this matter then see if thay will move on this as bad publicity will make it worse for ford

air for the inside of the car comes from the vent at the base of the windscreen or is recirculated inside the car
if you see what appears to be mist, fog or smoke from the ac vents ,it is extra cold air from the ac system that is seen as fog when it hits the air in the car
you will know exhaust fumes by the smell

Got kids? Crayon could be in heating/air system.

Possibly the vent line that routs fuel vapors from the gas tank to the charcoal canister has come loose. Check the hoses and lines around the fuel tank for leaks. There will be a fuel feed line to engine, a fuel return line from engine, and the evap. line or hose that carries the fuel vapors.

I emphasize with you on this problem. If you are smelling fumes you are inhaling car "exhaust" which is extremely dangerous as you know. I have a 1999 Passat that had a "fume" issue that baffled me for over a year. Your description of the conditions that you smell the fumes may not be complete enough for me to definitively say what your problem is but I will tell you what I experienced and discovered on my car. I only smelled the fumes when my heat or AC was on and the car was NOT moving forward. Also, if the AC recirculate button was on I didn't smell the problem as bad. So, what I found was that the car's emission control piping was leaking the exhaust fumes that bypass the pistons and go into the crankcase. These fumes are normally piped back into the intake manifold to be re-burned to reduce emissions. With a completed disintegrated rubber emissions pipe coming off the engine block, the fumes entered into the engine compartment which is sealed from the interior of the car. So, how did the fumes get in my car? Well, when waiting at a red light and with the heat or AC on (no recirculate) the fumes would fill the engine compartment and overflow out the wheel wells and wrap over the hood to the intake vents (near the wiper blades) of the car's interior air system. If the recirculate button is pressed with the AC on, the car's interior air (no exterior air) is recirculated inside the car to cool it faster and I didn't smell the fumes as bad. Also on windy days the fumes didn't get a chance to wrap over the hood and get into the intake vents. Because of the unique conditions that had to occur in order to smell or not smell the fumes it was a difficult problem to solve. By the way, the disintegrated rubber pipe was almost impossible to see and there is no real reference material to read that describes the location and depiction of the emissions plumbing. I hope this helps you!

This is usually a sign of a heater core that has a leak. check for low coolant level in your radiator. there is a condensate drain for the blower box, see if coolant is dripping from the drain under the truck. To make a temporary repair, after confirming leaking heater core, loop one of the heater core hoses back to the engine, bypassing the heater core. I say after confirming because the heater core hose nipples break easily when removing hoses. The smell in the cab would be a sweet smell from leaking coolant.

On a very humid day fog can be seen coming out of vents when using the AC. This would be a normal condition.

Sounds to me like a leaking heater core, probably just started. Quite an extensive operation to replace. If you happen to be in a cold climate, the windows will undoubtedly fog up. Hope this helps

YOU HAVE AN EXHAUST LEAK ON THE FRONT END OF THE EXHAUST SYSTEM.GET THAT FIXED ASAP! THAT IS CARBON MONOXIDE!