Re: Defrost without heat?

Posted by HH56 On 2011/9/7 15:38:23

Not really independent. It is in a separate compartment with separate controls but the second air valve on left side which controls the right side air vent has essentially 3 positions. There is a pivoting flapper valve in the middle of the large air tube at the "tee" directly under the heater box. When lever is "off" the flapper is angled one way which positions it to block the air. When in "air" it is straight so air flows past to the passenger vent and when in "heat", the flapper is positioned to block the vent and divert the air up the tee into heater box where it exits the heater/defroster plenum. As you mentioned, that direction is controlled by the lever on the right side. Setting the vent lever between the marked positions adjusts the flow accordingly.

Turning the blower on will increase air into the passenger compartment as long as the lever is in the "air" position. If the flapper is out of adjustment though, even if the lever is in the "air" spot it could position the flapper to restrict to the vent or to allow some flow into the heater box. In that case, if the thermal valve is working properly, heater core should be cold or just barely warm if the temp lever is "off" and it would still come out the plenum or defrost as ambient air.