While driving today at highway speed for about 5 minutes a burning rubber odor followed by white smoke infiltrated the cabin from panel air vents. Did not receive engine overheat signal. Pulled car over and checked engine, didn't see anything out of ordinary. Drove another few miles and same thing occured again. There appears to be adequate fluid in cooling system. The air conditioning has been non functional for over one year (bad compressor) and heating system was OK this past winter.

Any ideas?