Why is cold air blowing out for heat only on passenger side?
heating on 1997 Cadillac Seville STS
Your 1997 Cadillac Seville STS may use a "dual" climate control system. This will allow the passenger to select a different temperature than the driver. If the passenger side temperature door actuator were to fail in the cold position this would cause the problem you are describing. Please see the RepairPal article on automotive heating systems for more information - http://repairpal.com/i-have-no-heat-what-could-be-wrong.