Heater not working, defrost does

Surely my query has been answer many times here, but deang if I can find it.
I have a 1999 Ford F350 7.4 Liter Diesel turbo pickup; the vehicle's defrost setting allows air to be vented, but when I try
to vent air to the foot area or the chest area nothing comes out. I assume something is blocked, and that this happens often to people.
Is there a way to fix this? If you let me know the secret I will be ever grateful.
David
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Air stops coming out of ANY heater vents completely? Or the air remains coming out of the defrost ducts?

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On Wed, 19 Aug 2009 18:42:46 GMT, "Jim Warman"

Oddly enough, air comes out only from the defrost vents, no matter what setting the vent control is set on. Very strange indeed.

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First thing to check are the vacuum hoses uinder the passenger side dash.... these can be inadvertently disconnected... If that's OK, check the vacuum pump - located near the heater blower motor. With the vacuum hose unplugged, the pump should run continuously... if you connect a vacuum gauge to the running pump, it should shut off at about 15 or so inches.
Not odd... it is a very simple system.

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On Thu, 20 Aug 2009 07:07:15 GMT, "Jim Warman"

Thank you. I have checked the two wee hoses coming out of the pump and they are fine: as soon as the vehicle returns to where I am I will check the pump itself.
It seems like a very odd wayto engineer a vehicle's internal climate control.
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I dont see anything as being odd, per se... diesels don't generate any manifold vacuum, so a pump is required... On trucks with ESOF 4WD, the locking hubs are also controlled by vacuum...
Vacuum has been used to control HVAC functions for many years.
wrote:

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defroster only is the default setting when there is a loss of vacuum. so you either have a vacuum leak or your vacuum pump went bad. my money is on the vacuum leak. is it a four wheel drive with electric shift on the fly?? if so, i bet your four wheel drive don't work either, because one of the hub engagement lines broke.
oh, and by the way, it is a 7.3 diesel engine, not a 7.4

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On Wed, 19 Aug 2009 15:13:35 -0500, "Tom"

Greetings. It is manual shift, with hubs that lock manually and a seperate shift lever for low, high, and granny low. I will indeed look for a vacuum leak (the gods along know where to start looking). Maybe I can find a hose that is broken open, or a clamp that is missing.
Thank you a dozen times: I am in your debt, for life (which could be anywhere from an hourto 30 years).

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wrote:

I have seen some very cheesy vacuum switches used in the late 90's by ford. Not real familiar with that truck, but if the controller uses vacuum switches, I would look there first.
The strangest thing I have run across, is a fuel pressure regulator leaking fuel into the vacuum system, causing the heater to be stuck on defrost...
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On Wed, 19 Aug 2009 09:18:11 -0600, Desertphile

This vehicle has been sold, so I guess it is no longer my problem to fix the climate control. :-) Whew! That was an easy one....
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