Whenever I run my heater/defroster I get exhaust fumes (strong) coming into the car through the vents. I had the AC rebuilt during the summer and I can run it full blast without a problem no fumes. If I turn down the temp the fumes seem to go down. I haven't started to pull anything apart yet. Any suggestions would be appreciated.

 

Are you sure it's exhaust and not antifreeze? All the air for the HVAC system comes from the vent inlet at the base of your windshield. So you would have to have an exhaust leak (in the engine compartment) and then it would have to get past the rear hood seal and into the inlet.
A small leak in the heater core will act exactly as you discribe your problem.

 

Positive its exhaust. Big difference between exhaust and antifreeze. Since my last post I have done more investigating also. I only get the fumes while stopped. I don't think its as much exhaust as its possibly an oil leak dripping on to the manifold. I don't smell it with the AC because I have to turn it off or I drop all my amps. The altenator just can't keep up. I plan to get under the car and take a good look at the exhaust for oil burning off. Thanks for the reply

 

Sounds like your on the right track. I would get it up on a rack and check the exhaust connections forward of the doors for leaks, too.

 

Just a follow up. The PCV hoses deteriorated, so I was smelling fumes from the valves. The assembly cost $177 from the dealership or around $100 from a few GM places online. I fixed it with fuel hose and a "T" section for $17.00.