Ford F150 Ac only blows through defrost vents?

You either have a vacuum leak of a faulty mode vacuum actuator.

You can check the incoming vacuum by pulling the control panel out, and it should be the center vacuum tube. You can also check all the mode doors by applying vacuum to each tube with a vacuum pump.

See the diagram below for more help:----

1 — Steering wheel remote control switch assembly
2 19D888 In-car temperature sensor
3 19E663 Sunload sensor
4 19980 EATC module
5 18A318 Air inlet door vacuum control motor
6 19E624 Blower motor speed control
7 19E616 Temperature blend door actuator
8 18A318 Panel/floor door vacuum control motor
9 18A318 Panel/defrost door vacuum control motor
10 19E561 A/C cycling switch
11 19D594 A/C pressure cutoff switch
12 12A647 Ambient temperature sensor.

In many cases it is corroded vacuum line behind the battery.Dont forget to check there.

This basic details will help.Thanks.

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