Majority of the problem is two fold... first, your seals on the defrost
vents are bad... allowing cold air to escape to the windshield and causing
The second reason is that your defrost vent actuator has failed... but there
is two reason for this failure... One is if it is wide open all the time,
then it is your vacuum actuator that is bad. If you were accelerating or
going up the hill and noticed air coming out of the defrost is stronger,
then your yellow checkvalve is bad.
Lastly, is your air conditioner cold? If it is not, then you need a