Praying for help.  My 2006 Ford F150 was fine until I had the spark plugs and coils replaced.  At the same time I had the AC/Heat actuator replaced in the dash.  When I got it back, it ran great.... but there was a strange chemical/exhaust smell coming through the A/C into the cab.  Ive spent at least 6k trying to get someone to find the source (which includes exhaust manifold replacements and catalytic converter replacements).  To date, noxious fumes persist.  Its coming from the engine area, because I blocked the cowl air intake, and it gave a good amount of relief.. but not totally.  I burned out my Ac/Heat actuator by blocking the cowl intake.  Evidently my recycle dom cab is not working.  Been to Ford dealership three times, Firestone twice, and to the discount car repair place 6 times to diagnose and repair.  Ford, just kept my truck for two months and did nothing. Truly I know its unbelievable but they said each time that they had 600 cars to fix and 5 technicians :(. This all started when I had the plugs, coils, snd heat actuator replaced... Nov 2021.  What a nightmare.  A good truck, I cannot drive due to unknown source of fumes entering cab.  Any advice will be appreciated!