I have an early 77 and i need some sort of deforst before snow i have a problem with what i have now it takes like 12-15 mins to defrost my windshield and it is never warm in there . I dont think it's the defrost that clears my window i think it's motor heat coming up right under the windshield.

So I need help in what i should buy , a new heater core for heat or some fan cause even off defrost and on floor i have nothing blowing . I'm sure its one of these that is causing the problem

 

do u hear the fan running??????? if not then start there if it is running then its your heater core

 

Is there a constant wet stain on the floor of your truck? Maybe the heater core is out of fluid.

Maybe its just a slow heating core. My dad had an 86 truck that used to take 15 minutes to even start defrosting the windows. By that time the trip was usually over.

 

After starting up the pickup get out there and feel the heater hoses
for hot water flow and temperature.

Alvin in AZ

 

Sounds to me like your blower motor isn't running. The air blowing on the windshield should defrost it even without heat.

 

While we're on this subject, how difficult is it to get to the heater core on a '73 w/o AC? Mine is stopped up I think. When I got the truck it leaked a tiny bit, but it heated the truck, not it doesn't heat or leak!

 

I have simular issue with my 77 too. The heater hoses are warm to the touch, but the blower motor does nothing, no matter what speed you have it on. I checked the fuse which is in good shape.

That is all the further I have gotton at this point, been working on other issues, but starting look in to this issue. Any suggestions of where to start at? I am thinking of checking to see if there is power to the switch, and the motor. It does not have A/C.

 

Definately check for voltage at the switch, otherwise if the heater resistor was blown the blower would only work on "hi"

Also, replace the fuse anyways, I have seen plenty of "great" looking, pristine fuses that were actually blown.

Josh

 

to remove the heater core on a non AC truck drain the water remove the heater hoses remove the glove box door and liner, vent box,unplug the resister block. Remove the two nuts (7/16) on the heater motor under the hood then move over on the firewall about a foot and a half you'll see another nut on the firewall just about to the center, remove it unplug the heater motor and ground wire. Go back inside the cab some models have a brace under the dash remove it you should now be able to wiggle it loose on the studs it will come down a little now you can remove the cables on the heater box and pull it free at this time the heater core is accessible from the back behind the plate and the heater motor is also accessible.

 

Yeah, but. :)

Why pull -any- fuses tho?

You have electrical trouble...
So, you already have your meter out , right? ;)
Check all the fuses with your meter while they are in place.

Find the problem without disturbing anything, never know when you're
going to clear the trouble up moving wires etc. ;)

Not likely with a Ford but with an old VW the fuse holder itself could
cause the open. The bronze clips would get warm and loose all their
work hardened "temper". One of the best modifications I ever did to
VWs was replacing their sorry fuse setup with an after market fuse
block from the electronics store.

Same thing can happen to other types of electrical connectors too tho.

Alvin in AZ
ps- Great write up there PlowPusher! :)

 

It is not that hard to replace core and motor , did mine twice in last ten years , first time heater core was leaking , second time fan was making terrible noise and just replaced it , now I have new core and heater and heats up in minutes , replace heater hoses also , best thing I did when winter arrives . I was driving around for three winters until I figured out how to fix it and I lol of how easy it was , I felt stupid for three winters of freezing with the windows down to defrost windshield.

 

IF your 1973/79 F100/350 has factory A/C, it will also have a heater water valve.

This valve is spliced into the heater hose, passenger side rear, and is vacuum controlled.

It's also a total POS!

What happens is, it gets stuck, usually in the closed position, or partially closed.

D4AZ18495A .. Heater Water Valve (Motorcraft YG136)

Fits: 1973/79 F100/350 & 1978/79 Bronco w/factory A/C.

Fits ALL w/ or w/o factory A/C: 1971/78 LTD/Mercury Marquis // 1971/78 Mustang // 1971/76 Torino/Montego/Cougar // 1973/76 T-Bird & Mark IV // 1974/78 Pinto/Bobcat.

Still available from Ford.

MSRP: $28.72 / FTEpartsguy.com price: $17.23

 

I had a similar issue just the other day. I was wondering why I was getting around 11 volts to my signal relay, and nothing to my flasher/brakes. I put the meter on the fuses, they checked out great. Started poking around some more, checking bulbs, etc etc, still did not find the problem. I went back with a test light to verify that there was power at both ends of the fuse, and there wasnt. I was even further perplexed at the fact that there was power at one end(supply side), power on the fuse itself, and power at the other end of the fuse, but no power at the other terminal (the load side) I got a file and roughed the surface up a bit, nothing improved. I then started getting sparks when I would wedge the test light between the clips and the fuse, the lights would work. I knew I was close to figuring this one out. A small file was being useless in rectifying the problem, I wound up having to use a dremel tool with a grinding wheel on a low speed to polish up the metal. The supply side had corrosion, the load side had rust. After everything was clean and shiney, I STILL had problems. I put a new fuses in, my light problems went away. The old fuses needed cleaning, but they were old looking, so what the heck, fuses are cheap.

 

That was sorta my point, why dick around checking fuses when it's a simple matter to just replace it.

 

Replacing fuses is not always the answer. Replacing fuses in my case would not have fixed anything had I not thoroughly cleaned the contact points.