: AC only blowing out bottom vent

02-06-07, 07:10 PM
Any idea why the A/C in my '91 is only blowing out the bottom and not the vents?. I think someone at some point mentioned something about an A/C switch going bad. If you guys think thats the prob, where is it and how easy is it to change?. Once in awhile it comes out the vents for a short while and then stops and only comes out the bottom vent. Thanks for any help. :alchi:

02-06-07, 07:27 PM
I have the same exact problem with my 96 deville. Heat comes out the floor, defrost, and rear vents, but never the front vents

06-05-07, 09:14 AM
Yeah on my 78, the air only blows out the defroster and floor vents.

06-05-07, 05:11 PM
Vacuum leaks. It looks like the '91 Brougham defaults to floor with no vacuum. Most cars default to defrost and/or floor vents. I'll bet Destroyer, that you get air out vents on decel. Start at the vacuum tank (it could be cracked) and work your way in both directions. This applies to the '96 and '78 as well. The '96 tank is below the battery and the battery acid drips on the vacuum line usually.

07-07-07, 05:45 PM
I had this same problem and I know the 89 Brougham defaults to the floor when no vacuum gets to the programmer or the vacuum line harness is pulled from the programmer. (per the Caddy service information manual and actual experience) I now have the problem of partial defrost and full A/C through the dash vents at idle or low rpm/ light acceleration, but default to the floor when the engine is under heavier acceleration... I replaced about 20 ft of vacuum line under the hood and the old programmer which improved the rough idle, weak cruise control and full default to the floor problem I had to start with, but not the current intermittent climate control issues. Just replaced the vacuum tank, not better... Any thoughts from someone who has chased down this type of problem would be helpful... (sorry for the partial hijack!)