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A/C Service Tech Tip:
How to redirect the cooled air in late model GM cars
by John J. Brunner
Appeared March/April 2001 Cool Profit$ Magazine
© 2001 All Rights Reserved
1996 General Motors "C" cars (Oldsmobile 98 & Buick Park Avenue) and 1996 through 2000 General Motors "H" cars (Pontiac Bonneville, Oldsmobile 88, and Buick Le Sabre)—all with automatic air—may be blowing air conditioned air out of the defroster and heater outlets instead of the a/c vents. A likely cause is the weakening and subsequent crimping of one or more of the vacuum lines, or softened connector nipples within the A/C programmer. If you verify this symptom and want to correct it, here’s how:

Flexible nipples in this harness make it prone to failing. However, replacements extend back to 1985. Or, it can even be repaired.
(Click thumbnails for larger image). Figure 1. This is the male connection in the programmer showing flexible rather than firm nipples, and a broken nipple. This harness will not work! But with a little modification, you can replace it with one going as far back as 1985.

1. Release and fully open the glove box. This will expose the air conditioning programmer and multi color vacuum hose harness assembly. The vacuum source hose from the engine is black and connects to a violet flexible plastic tube going to the programmer vacuum connector plug.

2. With the engine running, locate the connector on the violet tube where it connects to the black vacuum hose. This connection is about six inches from the programmer. Disconnect the two hoses at this point to verify that there is indeed engine vacuum.

3. If there is not, you have a vacuum source problem. Identify the problem, repair it, and test again for vacuum and for proper air flow to the vents.
If the problem is solved, skip the rest of the steps and fill out the customer’s invoice. If there is vacuum present, you will have to keep searching. In all likelihood the problem is in the male vacuum connecter attached to the programmer.

4. Remove the 8mm nut holding the female plug and gently unplug the female manifold vacuum hose connector.

5. Check the male connectors. If they are soft and flexible, this is the problem. Often in addition to being soft one or more of these nipples will break off and remain in the female connector.

Clear plastic female connector, as it should look when replaced. Add the washer for strength.
Above: Figure 2. This shows the clear plastic female connector in place on the installed programmer with the suggested flat washer (circled in red) added for strength.

Below: Figure 3. This shows the interior of the opened programmer exposing the offending hose harness assembly. This assembly will need to be replaced or bypassed with 1/8 inch vacuum hose.

Interior of opened programmer showing the offending vacuum hose harness in place.

Unfortunately this harness assembly is not available as a service part. However, a similar programmer is used on "C" and "H" cars back to 1985.

Swap out the Harness from an older programmer
6. To proceed with the following repair, first remove the programmer from the vehicle. Trying to fix it while still installed will invariably lead to cracking the case.

Check this clear plastic connector for one or more broken nipples. If a replacement is not found, cut the connector off and bypass it with vacuum hose.
Above: Figure 4. This clear, plastic female connector may have one or more broken nipples. If a replacement programmer or harness is not used, and a repair is needed, cut the connector off and bypass with 1/8" vacuum hose.

7. If from a used programmer, you can salvage a male connector with firm vacuum studs, open the offending programmer and replace the harness assembly as shown in Figure 5. Put the cover back on the programmer and reinstall in the vehicle.

8. Before connecting the existing clear plastic female connector, you will need to carefully extract any broken nipples that remain. Now gently push the female connector onto the male connector you replaced in the programmer. Be sure to reinstall the nut using a flat washer. Without the washer the connection may not properly seal. (See figure 2)

9. Start the engine and set the controls for cool air. Remember, once the programmer is disconnected electrically it loses its memory. After re-connecting it and requesting air conditioning, it will take a couple of minutes for the system to function as directed. Retest and check again for proper airflow. If it works, you’re done and you can forget the repair below.

If a new harness cannot be found, cut off the black connector on the right and connect the vacuum hoses direct.
Above: Figure 5. The culprit: no one is sure why the hoses of this harness assembly become so soft that they crimp and cut off vacuum. But they do, and then chilled air is sent to the wrong vents. This assembly is the same one shown in Figure 3, but removed from the programmer.
If you can find an old programmer, swap out the harness. Look for GM #16258434 or AC Delco #15-72278 (fits a Buick). However, there are several programmer part numbers using the same harness. Don’t settle just for this p/n.

Plan B: Repair the existing programmer
If you cannot locate a replacement harness, plan on repairing the existing unit.

1B. Remove the programmer from the vehicle.

2B. Open the programmer and carefully cut the colored plastic tubes at their point of entry into the black connector.

3B. Cut off the clear, female connector. Reconnect each individual hose (color to color) using 1/8-inch vacuum hose.

4B. Complete Step 9 above.

I suggest that you also record on the repair order the inches of vacuum at idle. No amount of system repair can compensate for an engine that needs mechanical attention and is not producing adequate manifold vacuum. Please measure with a proper vacuum gauge.

Certainly, another option is just to replace the programmer. With a suggested retail price in excess of four hundred dollars, the option is a bit pricey, especially for an older vehicle.

However, with the hour’s labor as described above, you’ve found a repair that justifies a decent profit margin.                  $$$

John Brunner has a BS Degree in Automotive Technology. Recently retired from GM, he is now teaching, writing, and consulting on a limited basis. Phone: 480-969-4307
E-mail jjbrunner@qwest.net

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