ok...HVAC is short for Heating, Ventilation, and Air Conditioning. Basically, the box underneath the dash that houses the heater core, evaporator, and all the vents.
Look under the hood and check all of your vaccuum lines. Make sure none of them are brittle or broken (in your climate, they may very well be). Next, look for one that goes from the engine and disappears into a small box on the firewall. That box is a vaccuum canister...it stores vaccuum and releases it as needed. That canister also feeds the cruise control servo that is on the side of the engine, on the transmission.
On that line, there should be a check valve. It looks like a small disk that is inline with, well, the line. The check valve allows air to flow in only one direction...so in other words, only vaccuum should be present in the line AFTER the valve.
Hope this helps you out.
Welcome, downwardly mobile yuppies, to the dawn of the Age of Nefarious.
1993 SSEi - FrankenJinx - dead and gone.
1994 SSE (136K strong) - 180* t-stat,HD alternator, most unequipped SSE on the club, XM radio, Kenwood CD/MP3.
2006 Chevy Malibu Maxx LTZ - Custom 2.25" manifold-back exhaust w/FM-80. Probably the only Maxx with this system.