AC air blows through defrost vent only on Ford F-350 6.0 Diesel Engine?

Its a vacuum related issue.Noticed by many other care drivers too.



This is how your system works :----
Inside the dash there are vacuum operated motors that move doors in the dash to control air flow,the vacuum motors use vacuum to control them ,to open and close them.When the system has NO vacuum then it faults to defrost.So the problem is that you have no vacuum to the motors in the dash

Since you have a Diesel engine ,, it does NOT make vacuum like a GAS engine does, so a Diesel has an electric vacuum motor located under the hood by the right side fender

See the diagram below for better understanding:----

So check if this vacuum motor is working .For that turn the key on but do NOT start the truck,if you hear the vacuum motor running and will not stop running then you have a vacuum leak some where.
But if you do not hear the vacuum motor run,then pull off the vacuum hose on it.
If it does not run when you pull off the hose,then there is a two wire conector to it ,you should have power on one wire and ground on the other, if you have both ,,,then the vacuum motor is bad and needs to be replaced.

This detailed instructions will help you.

Thanks.

See below latest related solved problems.

Car AC Blows Warm Air ?

http://technoanswers.blogspot.com/2011/10/car-ac-blows-warm-air.html

How to test AUTO AC pressure?

http://howtobyme.blogspot.com/2011/10/how-to-test-auto-ac-pressure.html

AUTO Air Conditioning Troubleshooting?

http://technoanswers.blogspot.com/2011/10/auto-air-conditioning-troubleshooting.html

AUTO A/C COOLING PROBLEM?

http://technoanswers.blogspot.com/2011/10/auto-ac-cooling-problem.html

Fixing refrigerant leak?

http://howtobyme.blogspot.com/2011/10/how-to-fix-refrigerant-leak.html

How to locate Car AC Refrigerant leak?

http://technoanswers.blogspot.com/2011/10/how-to-locate-car-ac-refrigerant-leak.html

CAR AC INTERMITTENT COOLING?

http://technoanswers.blogspot.com/2011/10/car-ac-intermittent-cooling.html

What causes INTERMITTENT COOLING on Car AC system?

http://technoanswers.blogspot.com/2011/10/what-causes-intermittent-cooling-on-car.html

Car AC making Noise?

http://technoanswers.blogspot.com/2011/10/car-ac-making-noise.html

BAD ODOR ON CAR AIR CONDITIONER?

http://technoanswers.blogspot.com/2011/10/bad-odor-on-car-air-conditioner.html

Dodge Caravan AC Heater Control only works on high mode?

http://schematicsdiagram.blogspot.com/2011/12/dodge-caravan-ac-heater-control-only.html

Honda Civic Blower Motor Only works on high mode?

http://schematicsdiagram.blogspot.com/2011/12/honda-civic-blower-motor-only-works-on.html

How to Test and Replace Blower motor on car?

http://repairhelpcenter.blogspot.com/2011/12/how-to-test-and-replace-blower-motor-on.html

How to Replace Blower Motor Wheel?

http://repairhelpcenter.blogspot.com/2011/12/how-to-replace-blower-motor-wheel.html

How to Replace Blower Motor on 2008 Honda Odyssey?

http://howtobyme.blogspot.com/2011/12/how-to-replace-blower-motor-on-2008.html

How to Remove Blend Door Actuator on 2008 Honda Odyssey?

http://howtobyme.blogspot.com/2011/12/how-to-remove-blend-door-actuator-on.html

How to Remove Passenger Side Blend Door Actuator on 2008 Honda Odyssey?

http://howtobyme.blogspot.com/2011/12/how-to-remove-passenger-side-blend-door.html

How to Remove Driver side Blend Door Actuator on 2008 Honda Odyssey?

http://howtobyme.blogspot.com/2011/12/how-to-remove-driver-side-blend-door.html

Blower motor Resistor shorting problem?

http://schematicsdiagram.blogspot.com/2011/12/blower-motor-resistor-shorting-problem.html

Heat blows cold on drivers side and hot on passenger side?

http://schematicsdiagram.blogspot.com/2011/12/heat-blows-cold-on-drivers-side-and-hot.html

Hot air on the driver’s side vents only?

http://repairhelpcenter.blogspot.com/2012/01/hot-air-on-drivers-side-vents-only.html

Ford F150 Ac only blows through defrost vents?

http://technoanswers.blogspot.com/2012/01/forf-f150-ac-only-blows-through-defrost.html

Dodge A/C come out of defrost vents only?

http://technoanswers.blogspot.com/2012/01/dodge-ac-come-out-of-defrost-vents-only.html

Ac vacuum line on dodge cummins?

http://technoanswers.blogspot.com/2012/01/ac-vacuum-line-on-dodge-cummins.html

Ford ranger AC blows cold through defrost vents instead on cabin vents?

http://technoanswers.blogspot.com/2012/01/ford-ranger-ac-blows-cold-through.html