A/C "Mode" switch not working

[IntrigueHater]

In an attempt to draw more input, I'm reposting this with a new title that is a little more descriptive. My 98 3.8 is blowing air from all the vents, and does not change regardless of what mode I select. I also get a clicking noise when I hit the rear defrost button. AND. My DRL headlights flicker every now and again. The dealer said the A/C controller needed to be relaced, but I swapped it with a known good one and am sure that's not the problem. I've checked all the vac lines under the hood and all are in good order. The A/C blows cold as it should, it just comes out of every vent. So would this be a vacuum issue or an electrical issue? From the schematics it looks like the changeover controls are vacumm and electronic. I'm probably going to try cleaning and/or replacing the ingition switch, since others have reported success with that when they've had odd gremlins in the HVAC system. But is the "mode" door that changes the air output direction replaceable? I know the blend doors are based on other posts here.

[brcidd]

Put a vacuum gage on your vacuum line underhood-- takes at least 15 in-hg to move the doors-- the norm is more like 17+ in-hg... This is most common problem of mode door/actuator problems...most likely the vacuum line is detached from vacuum canister in wheel well- behind driver's side front wheel-- trace your lines-look closely where vacuum line routes down by battery-- you'll probably find the broken vacuum line....I've fixed many W-cars like yours....this way.

[IntrigueHater]

The battery in mine is on the passenger side. Or is there a line on both sides I need to check? Cause when I traced it it looks like hte lines ran across front and back of the engine compartment.