Third Gen Air Conditioning Problems

Q: How come air will only come out of my defroster vents?

A: These "cables" are actually small plastic vacuum lines from the A/C controls which actuate small vacuum "motors" underneath the dashboard next to the firewall (they look like small silver tops with a small color hose attached to them). If you pull out the A/C control panel, you will see different colors corresponding to a control setting – blue for defrost, orange for floor heat and so on. The "motor" moves the control gates for directing the airflow via the dash and console vents and so on. The usual problem is that the vacuum source line gets broken or pinched from the vacuum box (on the firewall next to the washer assembly) to the controls. When the vacuum source is interrupted, the controls freeze on the last setting of vent, defrost, etc since there is no vacuum source to actuate the "motors". Follow the main vacuum line (usually a stiff black plastic line) from the box to the original vacuum source (A/C system or manifold) or from the box to where it enters through the firewall to your control switch to see if either one is broken or pinched. This is what you hope is the source of the problem.

Next, check your vacuum line to see how it connects to the harness with the color coded lines (see the Chilton repair manual for the difference between early and later f-body a/c system controls). If any line is broken, it is usually another potential vacuum leak as it is all one piece. This can happen when installing a new stereo system as everything can get jammed up behind the console. These can be repaired by splicing in 3/8th inch rubber hose. The problem you don’t want is a broken connection at the control panel. Since it is a one piece vacuum harness, it can mean removing almost the entire dash, seats, and front console to confortably get at all the motors to hook up the harness and the corresponding lines to the motors.