At 11:13 AM 5/24/2003, Charles McGuire wrote:
Vacuum Troubleshooting: While here I also want to check for vacuum leaks in the control system. I have a new Mity-Vac. Do I just apply vacuum to the other side of the check-valve by the brake booster and see if all operates OK? What is best way? Just replace all stiff / old hoses? (Maybe just take off all "unnecessary parts and make it a track car?!)

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Remove the side panel from the driver's side of the center console. Look at the forward end of the opening, and find a bundle of colored plastic tubes.

Get a few inches of small rubber line that fits snugly over the plastic lines.

Using a sharp razor knife, cut the orange line. You now have an upper end that disappears up into the dash (to the vacuum actuators), and a lower end that runs forward into the console (from the vacuum solenoids). Use the MityVac to apply vacuum to the upper end, and see if the vacuum actuator holds vacuum. If it leaks, plug the BOTTOM end (that goes to the vacuum solenoid) using the small rubber line and a piece of a nail or something similar. You can just leave the upper end open. If the actuator holds
vacuum, use the small line to splice the two ends back together.

Repeat the process on each of the lines except the black one, which is the source line.

The white line operates the heater valve - if it shows a leak, fix the leak or replace the heater valve - you need for it to be functional.

After you have disconnected any leakers, the rest of the actuators will now work, provided that you have a good strong vacuum on the black source line. If you don't have a good vacuum here, check the rubber cross and the black/blue check valve near the brake vacuum booster, and check the line running to the cruise control in the front fender for leaks.

Wally Plumley
928 Specialists

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1) Move the driver's seat all the way down and back. Remove the console side panel.
2) Find the bundle of small colored plastic tubes near the driver's right calf position. Get some small rubber or plastic tubing that looks like a snug fit over the colored tubes.
3) Using a sharp razor knife, cut the orange tube. Apply vacuum to the upper end - the end that runs up into the dash. If the tube will hold vacuum, splice the tube back together with the rubber or plastic tubing. It is not likely that the upper end of the orange tube will hold vacuum. If it doesn't, use the small rubber or plastic tubing and a small plug to plug the other end of the orange tube - the end that runs forward to the vacuum solenoids. Don't bother to plug the end that you tested, and don't bother to test the end that you are plugging.
4) When and if you get a round tuit, replace the center vent vacuum actuator. Until then, the HVAC system should work better.
5) If you still have some HVAC issues (hot air all the time, air coming in all the time, etc.), repeat step 3) on the green, yellow, and blue tubes.
Don't cut or test the black (source) or the white (heater valve) tubes. If the heater valve leaks vacuum (or coolant), replace it.

Wally Plumley
928 Specialists
www.928gt.com

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Tubes at the vacuum relay area for a 1987/1988:

Black (main)
Yellow (foot well)
Green (defrost)
White (heat)
Orange (comb)
Blue (Re-circ)