A/c changes to defrost when i put truck in 4 wheel drive

some a/c / heater actuators are controled by vacuum vacuum line may be pinched or broken when you did your repair,diesels have vacuum pump that suply vacuum for differant things,because diesel engine can not produce vacuum it self.if vehicle happens to have electric acuators then something may have been left unpluged or you may have blown a fuse

Blower Motor
See pics bellow Removal

1. Disconnect the electrical connector from the vacuum pump (7.3L diesel engine).

1. Remove the bolts (7.3L diesel engine).

1. Disconnect the vacuum hose and remove the vacuum pump and mounting bracket (7.3L diesel engine).

1. Disconnect the speed control servo connector (5.4L and 6.8L gasoline engines).

1. Remove the bolts and remove the speed control servo (5.4L and 6.8L gasoline engines).

1. Disconnect the connector.

1. Remove the blower motor ventilation tube.

1. CAUTION: Carefully remove the blower motor so as not to damage the wheel.
   Remove the screws and remove the blower motor.

1. CAUTION: If the wheel is to be reused, clean the corrosion from the shaft end prior to removing the wheel.
   Remove the wheel from the blower motor.
   1. Remove the push clip.
   1. Remove the wheel from the blower motor

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Installation

1. Follow the removal procedure in reverse order.

Assuming you have vacuum controls at the heater control head, you have a classic vacuum leak in the hose from the engine intake manifuold to the control head, or the vaccum storage canister somewhere in the engine compartment. It is required to fail to defrost by law.

Climate Control Assembly
The climate control assembly has 3 system controls:

• The function selector switch combines a vacuum selector valve with 2 electrical switches to supply battery positive voltage (B+) to the blower motor control circuit and the A/C clutch circuit (if equipped).

Vacuum Control Motors
The 2 vacuum control motors:

• are actuated by vacuum from the function selector switch.
• position the plenum doors to direct system airflow to the vehicle's interior as determined by the function selector switch setting.

The vacuum reservoir is behind the driver fender well, black plastic ball.

If you have diesel, then you will have a vacuum motor under the hood.

please rate if this helps.

blower motor relay is stuck, cheap to replace

Sounds like the "Blend Doors" are not completely closed (or opened). The Blend Doors open and close to direct the air from the blower motor to the vent selection you have made on the control panel (defrost on windshield, floor, front, etc) You may need to try various selections to see if the blend doors actually open or close. If no changes, it could be a blend door actuator failing.

it could be the electronic blend door motor. Try not changing any settings for a week and see if the fuse blows. Leave it on floor/defrost.

usually it is the bearing in the blower motor going bad. I believe it's a 25 amp fuse. The motor draws about one amp for each volt increase up to 14 volts.

go to our site for more help.

http://groups.yahoo.com/group/villagerquest/

Take the actuator off and see if it is moving fully to all positions. While it is off see if you can manualy put truck in 4 low and 4 high.

Check vacuum lines on firewall for leak, check all vacuum lines if one on fire wall is ok , doors work off vacuum

Try selecting 2 wheel drive and reverse for 20meter .

well can get a new car that 6557 code is a blower moter code