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

Reply to
Desertphile
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Air stops coming out of ANY heater vents completely? Or the air remains coming out of the defrost ducts?

Reply to
Jim Warman

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.

Reply to
Tom

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

Reply to
Desertphile

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).

Reply to
Desertphile

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.

Reply to
Jim Warman

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...

Reply to
James Patterson

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.

Reply to
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....

Reply to
Desertphile

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.

Reply to
Jim Warman

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