One problem related to defogger heater has been reported for the 1999 Chevrolet Venture. The most recently reported issues are listed below.
I own a 1999 chevy Venture. In the past two months the heater core has gone out three times, the first time being the original that lasted six years. When it goes out, it fogs the window up so bad that driving is nearly impossible. Chevy has sent out service bulletins that note a problem with electrolysis that rapidly deteriorates the heater core. The heater cores are chevy parts. There seems to be no permanent fix available. The last repair made today included the addition of a grounding cable.