I have a vacuum hose off by the wiper motor ('01 GMC Jimmy 4WD). It's a 3 way vacuum with a check valve. The plastic line & the long hose to the engine is OK. It's the 4 inch long hose that's loose. (AKA no lower heat duct operation). I can't find where it connects to?

 

If you have a mechanics mirror, you should be able to use it to locate the missing vacuum hose. I'm betting that it has fallen down under the brake booster.