Re: 1955 defroster not working.

Posted by HH56 On 2018/2/21 10:08:27

In addition to the cardboard ducts O_D mentions there is a cardboard like flapper valve or air diverter inside the plenum. When the cardboard ducts are inspected also check to verify the small crank arm visible toward the right side of the exposed front surface of the plenum is moving when the knob is moved. If it is and ducts are OK then most likely the flapper material has come loose from the crank shaft and is not moving properly. The flap has to move down and cover the heater side before air can flow thru the defrost side.

If things look like they are working you can remove your plenum and take the cardboard back off to see what is happening or if there is a problem see if it can be repaired. Believe the back is stapled onto the plenum so you could take it off and fasten back with other means. You can also buy a new plenum from Quietrides if you don't want to mess with fixing yours. I would call and verify the flapper assy is present and operational in the new plenum because I believe when Cli55er was working with them on doing the repro it was a question if it would be included or if some of the old pieces would need to be moved.

Here is an illustration of the repro and also a bit from the service manual on the function of the flapper.

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