1975 Cadillac Convertible Cabin Airflow Issues

[rustytarbs]

Hi, I have a 1975 Cadillac Convertible and although the air-con blows icy cold air, all the air(or the vast majority of it ) blows out the floor vents. Also the heater doesn't seem to work at all, just blows air, again mostly from the floor vents. Can anyone help me fix this, or is it a major job involving the removal of the dash? Kind Regards, Russell

[The Tassie Devil(le)]

G'day Russell,

I would be initially checking all vacuum hoses, and there are many behind the dash as well.

These unit controls rely on a lot of vacuum motors to operate the multitude of operations.

But, someone more knowledgeable than I will come to your rescue shortly.

Bruce.

[cadillactim]

Russell

First thing to check is operation of programmer. It is located behind the glove box. You can see it looking from the floor behind the glove box. It is a black box with several vacuum lines and wires plugged into it.  On the lower left corner of the programmer you will see a slot about 2 inches long, 1/4 inch tall.  Take a flashlight and you will see "A/C" on one end of the slot and "HEAT" on the other end. Through that slot you will see part of a metal bar (which is connected to the vacuum motor in the programmer).

Now, with the car running, set the temperature dial to 85, lever on AUTO.  That metal bar in the slot should move all the way to HEAT within a minute.  Then set the dial to 65, and the metal bar should go to A/C.  If it does these two tests, your programmer is probably okay.

If the metal bar does not move all the way to HEAT, first make sure you are getting vacuum to the programmer. Unplug the big vacuum connector plug and check for vacuum at the solid black (no stripes) vacuum line. Many of the programmers have etched in the cover "SOURCE" at the vacuum connector, which is the line you want to check for proper engine vacuum.  Also make sure you are getting battery voltage to the programmer at the small yellow wire. If you have vacuum and voltage, reconnect the vacuum plug, then unplug the ambient sensor on the evaporator case.  If it still won't go to HEAT, then you have a programmer problem.  If it will go to HEAT, but not A/C, then take a jumper wire and jump the two wires that plug into the ambient sensor. Programmer should go to A/C.  If not, then a programmer problem.

So if the metal arm does not move properly from A/C to HEAT, and you have proper vacuum and voltage to the programmer, then your programmer is bad.  If metal arm moves properly, but the air flow is to the floor, then your problem is most likely a bad rotary valve in the programmer (which is rare), or a bad vacuum actuator that is leaking, or a leaking vacuum line to the actuator(s). 

When the metal bar in the programmer is all the way to A/C air flow is through the dash vents (dash lever on AUTO). When metal bar is all the way to HEAT, air flow is on the floor.

Cadillac Tim

[Jeff Wilk]

Cadillac Tim......that is the most amazing and clearly described test for these systems I have ever seen.  THANK YOU!!!!!!  You should publish a book with more of this simple to follow guides to diagnose issues.  Thanks again.....


J Wilk

["Cadillac Kid" Greg Surfas 15364]

Russel,
I might suggest two other things to check.
You say that the air is blowing cold but through the "heater" vents at the floor.  Check to see that the heater, water lines are connected and that any shut off valve in the line is opened.  Any "open" (connection or sensor) in the sensor string will cause the programmer to stay at the full heat  position, and I have seen where rather3r than finding and fixing the sensor string circuit, people have installed shut-off valves in the hot water line to shut off the heating core, and "lived with" the floor delivery.
One of the most common sources for the "open" condition in the sensor string is the disconnection of the "in-car" sensor in the dash.  Sometimes when either replacing the dash or working behind it this connection is inadvertently disconnected. One of my most successful techniques when working on these ATC systems is what I call the "disre" technique.  Tghat is dis connect and reconnect.  It works on vacuum as welll as electircal control systmes and fixes what is wrong (disconnected) about 75% of the time.\
Greg Surfas

[cadillactim]

Jeff

I do have manuals on these systems, from 1964-76.  Tim

[rustytarbs]

Well I must say that I am floored with these responses, I didn't expect anything so thorough! Unfortunately I am busy with work for the next week and my car is garaged at a friends(no space at my little place) so I wont be able to go over these steps for a little while, but I just want you guys to know I am so grateful and very impressed with the responses to date. Will be sure to let you all know how I go when I do have a look, Kindest regards, Russell