In the same rainstorm that I discovered the windshield leaks in my '66, I also found out that the defrosters are, as my father liked to say, a dead man breathing. I'm pretty sure the hoses are intact and hooked up correctly.

The motor seems to really blow, but when flipping the lever on the housing from "on" to "def", I get NO change in CFM from the defroster vents, and what's there is barely detectable.

I am capable of removing the heater assembly and going thru it to make sure things are in working order, but what I wonder is, are the defrosters in these trucks adequate when working properly, or am I seeing the best it's going to do?

 

It's probably about as good is it gets. Defrosters in the old days were pathetic.

Check the heater box and all the hose connections all the way up to the outlets. Part of the problem with the old systems was the lack of air tight connections. Once it's all tight, it will still be a wimp compared to a new car.

Since 1974 or so, Fed auto regs have mandated defrosters live up to their name. Cars with AC use the AC to dry the air, making them able to clear the windows in no time. If you are used to new car performance, it's going to be hard to be satisfied with your old one.

As for the windshield, pony up for a removal and proper reseal job at a window place, if you can find one that you trust. External silicon and other efforts are not going to make up for dried out gaskets.

 

The defroster in my 63 will blow yer hair around.

 

I haven't taken an F100 heater box apart, but other old car heater boxes that I have taken apart have a valve that diverts the flow to either the heater (floor) or up to the defrost. The valve is a flat steel plate wrapped with foam. If the foam is deteriorated then the valve won't seal the heater outlet and force the air up through the defrost ducts. In the past, after I've put new foam inside the heater box, the difference has been amazing. Seal kit is cheap but it is time consuming taking the heater box out and apart.

 

I thought my 65 had weak defrosters too... like almost non exsistant weak.

monkey with the flap lever that directs the air to the defroster. I moved mine just a bit past where it "stopped" and bada bing, great defrosters.

you should be able to reach those levers pretty easy.

 

brider, In 40 years you can get debris in the housing. The lever that you move is just a deflector paddle, (same air flow for both directions). Gently unlatch the tabs on the hose and slide them off the housing, make sure they are open. Next turn the fan switch and ign key on. check the flow with the deflecter in all positions. Pull the big hose off on the intake side and make sure it is free & clear as well. The heater motor can be pulled also if needed.

Let us know what you find.

John

 

Thanks for the tips, guys. I went thru the same thing on a '71 Landcruiser, so I know what a mouse nest in front of the core will do.

The heater project will have to wait until the weather turns colder. I just noticed it during the recent rainstorm, and I don't like driving it in the rain anyway.

Basically, I like this forum for a place to vent my little truck troubles, 'cause nobody else I know (especially my wife) cares.

Thanks for being there, guys!

 

Brider, and all:

My defroster suffers the same anemia and all the posts on this subject are really helpful. I second your comments of appreciation for all who take the time to write. It's great .. thanks.