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
Air stops coming out of ANY heater vents completely? Or the air remains coming out of the defrost ducts?
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.
Oddly enough, air comes out only from the defrost vents, no matter what setting the vent control is set on. Very strange indeed.
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).
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.
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...
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.
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....
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.
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