I have an 82 F100 in very good shape. When it rains, the windshield fogs up and the defroster will not clear the windshield at all! I have great airflow, and there's very hot heat when the selector is moved to hot. Could it be that the airflow is not directed properly at the windshield? Seems to be hitting the windshield fairly low, but there is a great deal of air moving. I can crack the window and it helps a little, but I still have to keep wiping the window to be able to see. I don't think it was like this when I got the truck last year, but I can't remember. It's not even like it will clear a little port hole for me to see through...LOL.

Anyone else ever have this problem?

 

There could be something down in the small defogger duct openings affecting the way the air comes out. It could still be allowing alot of air flow out of the unrestricted parts, but not in the right amounts or pattern.

 

Or it could be the heater core has a leak ad you're trying to clear the window with steam.

Do you have air conditioning? If so, two things to look at:

1) The vacuum lines controlling the vacuum motors that operate the flaps (change air flow from floor to face vent to defrost).

2) The hinges on the blend doors can break, and air will be distributed < wherever > .

 

If it were leaking, would you be able to smell coolant?

 

I had an 88 F150 with a failing heater core that poured DENSE fog into the cab when set on demist, with no real antifreeze smell, until the leak got worse later.
I don't remember the windscreen misting up though - just thick,white fog, like smoke.

Is it good airflow to the windscreen, or just the floor?

 

Same here. My leak eventually got bad enough that it was foggy in the truck. I never smelled antifreeze until it got that bad, although I never had a problem defrosting the windows until it got that bad.

If you have factory installed A/C it wouldn't take long to take a look at the heater core.

 

Two problems can cause this...

A leaky heater core as suggested..., although it should fog the windshield rain or shine. When mine went, my windshield could be dry, turn the defroster on, and it would fog up.

If your core doesn't leak, or you have never done this proceedure in a long while, you may have leaves and debris in your duct system, which can cause a simular problem.

Fresh air comes into the heater and/or a/c system through the cowl. (It's right below the windshield with the slots and holes for the wiper arm pivots.) Leaves and debris can enter the heater through those slots. It will block the heater ducts at the bottom of the cab at the water drains on each side. The water when it rains will also enter the cowl, hit the leaves and produce moisture inside the heater system. Worst case scenerio is this problem can cause a heater fire.

With trucks without factory A/C you will have two fresh air vents located on both sides of the cab just under the dash where the kick panels are. Remove the kick panels, remove the vents, then stick your hand down into the hole and pull up and clean any debris found.

Trucks with Factory A/C you will not have these vents, however remove the kick panels and you will find the inspection plates. Remove the plates and stick your hand down inside and clean it just like mentioned above.

For a final measure remove the heater fan motor from the heater box and see if there is any debris around inside, especially around the heater motor resistor.

hope this helps...

 

Thanks a lot everyone, I believe this is the problem as it is fogging the windows even in dry weather. I am just now starting to smell antifreeze as I first turn the system on. Is the heater core difficult to change on the truck? I've changed a few on older Fords that were a pain in the keister. Thanks!

 

It's easy if you have AC, I understand one can access it by removing the glove box.

Without AC, it's an ordeal that requires removing the heater box from the firewall (which requires removing the cowl).

 

Luckily I have air conditioning.

 

It is very easy on a A/C truck, too easy you say to yourself after you have completed the job. There have been some threads where people have had trouble making the aftermarket heater cores fit though. Just keep an eye out for that.

 

On the aftermarket cores, if the top and bottom tanks are not rounded it will probably NOT fit. And most of the aftermarket aluminum tanks don't have.

 

I bought one at Napa, so we'll see. Where is a good source for a core if the one I bought does not fit?

 

The best source brand is Motorcraft.

 

It's kind of easy to tell if it will fit. If it's aluminum and the top and bottom tanks are NOT rounded it probably wont fit, at least it wouldn't on my truck. On my truck the the housing that the tank went into was rounded on top and bottom to fit the factory tank so the squared of tanks on the aluminum units would not fit into the housing. I've heard Rock Auto had the right ones on line but can't say for sure. I've been told only the copper/brass units will fit correctly. What I did was pick a used factory one up from a friend that owns a JY till I can track down the correct new one.