03 mustang cold air coming out the defrost vents

SOURCE: 1998 Mustang - AC blows only through Defrost vents

You probably have a vacuum leak on the passenger side. its a small plastic hose some times they come unpluged from the engine. or brake.

SOURCE: Vent control

You have a vacuum leak.Defrost is the default postion(no vacuum).
See if you can locate the small black vacuum line that goes inside the vehicle on the passenger side near the heater core. The trace it back,should see it going to a canister then to the intake manifold.Make sure it is not disconnected or broken somewhere.

SOURCE: PROBLEM WHEN SELECTING THE DIRECTION FOR THE AIR

Sounds like you have a supply vacuum problem. When you lose supply vacuum to the control head it defaults to defrost.

SOURCE: Ford F150 2003 When I press the max cool on the AC the air comes out of the windshield defrost vent iinstead of the cabin vents and is not as cold as it use to be. Summer in Texas Help !

You did not mention if the system you have is electronic(digital control) or manual(control knobs) but what your problem is, is a vacuum leak. Defrost and heat or the default postions for no vacuum. If it works ok until you press max air Then you will need to check the outside blend door vacuum motor. It will be the white vacuum line going from the control head.

SOURCE: My 95 Ford Mustang will only blow air out the

check for a vacuum leak from the vacuum source on the engine to the heater control head.


defrost is fail safe mode.

A/C Vacuum Reservoir Tank and Bracket Removal and Installation

1. Open the glove compartment (06010) .

1. Working through the glove compartment , remove the vacuum reservoir retaining screw.

1. Remove two vacuum hose tubes from the check valve and remove the A/C vacuum reservoir tank and bracket (19A566) .

1. To install, reverse Removal procedure.
   
   A/C Vacuum Reservoir Tank and Bracket