Heat Vent defrost blower

[T Col]

Hey folks - anybody got a diagram or anything for the heat/air system, mainly just the fan? The fan in my sins 79 is blowing to beat the band but nothing is coming out the vents, I think the switch is good because it tries to change to the different functions and turns off but nothing comes out. Figure it is a vacuum issue with a valve but don't want to pull the whole truck apart until I know where I am going, thanks

 

[BuzzGun79]

From my experiences...there are 2 vacuum diaphrams located on the heater box,one controls the temp..the other controls vents.removal of the glove box does aid in viewing...also check the vacuum hoses for crack and leaks.I have also experienced a broken off port in the back of the heater/ac control panel.once the glove box is removed..start the vehicle and work the panel while looking at the diaphrams see if they are operating.Heater box door flaps could also be worn or stuck.

 

[fatherdoug]

http://www.fordtruckfanatics.com/forum/showthread.php?t=31386

Can also take a look at the link above. It is the scanned heat, A/C section from the 1978 Ford shop manual.

 

[T Col]

Thanks for the tips and the scan - just my luck did not see any of the models that looks like ours

Weird thing is that when I manully operate the flaps I still don't get any changes course I am probably missing one somewhere.

I am suspicious of another thing though ---- on the drivers side fender well under the hood, a "doo-hickey" much like a toilet bowl ball that has what I think is a vacuum line going back to the control panel ---- it has a crack in it and isn't that a major part of the vacuum system????

 

[fatherdoug]

That "toilet ball" is a vacuum reservoir. Is it plastic? If it is, it is probably an addon or a replacement from a previous owner. For 79, Ford was still using metal "tomato juice" cans for vacuum reservoirs. There might also be one under the driver's front fender. There will be a vacuum hose running along the fender well and through the fender.

Are other things affected by lack of vacuum, such as power brake booster, cruise control(if you have it) or engine operation/transmission operation?

 

[Fellro]

The vacuum reservoir won't affect the brakes, as the leak is too small, but it will definitely make the blower only put air out at the defroster.

 

[T Col]

Hey I remember the coffee can on my last 79- anyway, that "ball" does have a crack in it around where the line goes in it, looks like they tried to hot glue it back in but I can easily move it in and out. Son said the other day it actually came out of the defrost like he wanted for a little bit and then went back to nothing again,,,, think its smart enough just to got get a new "toilet ball" just in case before I loose my mind???? Surely those are cheap enough to change just in case (oh by the way notice no other problems with any other functions) - thanks

 

[Mil1ion]

 

[fatherdoug]

All the above is linked in Post #3.

 

[Mil1ion]

I know but IMO it is better served right on the thread

 

[vls]

Have you checked to see if your ducts are full of leaves, pine needles, etc? The louvers in front of the windshield have no screen to keep crud out and they can't be removed. The gunk slides down both sides into the space at the rear of the front wheel wells, where it eventually clogs any intake air. I have to clean mine every year. Taking off the plastic vent covers by the kickboards is the best way to get at the ducts.

 

[Mil1ion]

My guess it is the blend door actuator.