I am getting cold air at the floor and defroster vent but none out of the front vents no matter where the selector is.

It was working properly yesterday.

Any idea or suggestion ?

 The mode selection is done through a series of air doors that are operated by vacuum. When there is either a partial or total loss of vacuum, the system will default to either defrost or on some vehicles, heat. Acceleration can also have an effect on the doors for the same reason.

Look under the hood for a small black plastic hose coming through the firewall. Follow it to the vacuum source looking for any breaks, cracks or leaks. Also follow any other lines that branch off because they may go to a vacuum resevoir (storage tank) and a leak there will cause the same problem. Using a vacuum gauge to determine if you have full vacuum at any given point is the best way to find it. You can cut into the line anywhere and splice it back together with a piece of vacuum hose. Find the broken line, you found your problem.




78 Corvette Pace Car For Sale-18k mi orig-Florida

As usual, you hit it out of the park. The small line going to the firewall connection got bumped and cracked when the oxygen sensor was replaced.

Spliced and it's now working properly - THANKS .

Glad it worked for you. Thanks for posting the resolution.




78 Corvette Pace Car For Sale-18k mi orig-Florida

It wastes ink but they are good for wallpaper! Great fix!

T
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Tom Greenleaf - MetroWest, Boston