BCB

No mater where i turn the slector on the dash for the air to blow in the cab it blows through the defrost vents and the floor vents... whats wrong? what di i need to check?

Break Away

Vacuum leak...?

AggieJustin

Are you sure you're getting air at the floor vents? If you lose vacuum to the selector door, you'll only have air at the defrost vents. If that's the case, you need to check the vacuum lines under the hood and the line through the firewall to the vents.

If you have air on both the floor and defrost and it won't switch, then your selector door may be jammed up.

kd460

Yes, like mentioned check all lines for leaks. When my 97 did that it was the vacuum servo located under the dash at the center hump just to the right of your right foot if you sitting in the drivers seat. Follow the hump up about midway (maybe a litte closer towards the seat than in the middle) is a silver looking cannister with a plastic lever (I think white) anda vacuum hose connected to it.

With truck running and selected to blow at your feet, reach up and move the lever by hand. If manually moving it makes it work the way it's supposed to, then most likely the diaphram in that servo is shot. You could vacuum test it to be sure. It is still possible you have a leak in one of the lines, but most likely that is it. Check the selector switch behind the dash before checking the servo, check for line leaks before checking the servo. In other words, make sure it's not a simple leak before replacing the servo.

That servo is one of the few (I think there is 5 or 6 servos behind the dash) that you can change without taking the dash apart. It's a little tight, but you can reach up there and get it out to replace. Just be careful the linkage can break easily.

I picked one up at the junkyard and it's been working good since. If you get a junkyard servo, bring a vacuum tester or a piece of hose (to suck) and check the diaphram before buying. I used a large sryinge (from work) and a piece of hose to check mine before buying.

Sometimes they just fail, but, the 97's had a probblem with oil being introduced into the vacuum lines from the vacuum pump system. The oil gets in there and that servo is the first one to recieve some of the engine oil. The oil can cause the servo diaphram to rot out. I had that problem, and installed a small clear fuel filter in the vacuum line coming out of the pump to serve as an oil trap. I believe there was also a recall but not on our trucks?

Probably more info than you wanted, but, hopefuly it helps you figure it out and fix it, and prevent it from happening again.

Do a search on vacuum servo and you will get much better info. (vacume, vacuume, vacuum). KD