vaccum leak?, HVAC controls not switching position

[pwrplygoal99]

My HVAC controls are not working, the fan motor is working fine, but air only blows out top(defrost) & floor, nothing out of vents regardless of switch postion. I was told it could be a vaccum leak to the Contol panel. Whats is the best way to track it down? i found a broken vaccum line valve under the hood, replaced it with no change on HVAC control panel.

 

[challengermike]

I just had the same problem.I pulled the bolts out of the control that holds it to the dash.Then i started the car and started reaching around the control unit untill i heard a change in vac.I found that there is alittle black valve on the drivers side of the control panel that was leaking.I just popped the top of it off and there was a rubber flat washer inside.Mine looked like somebody put it together wrong.The washer wasnt sealing anything where they had it.I cant remember exactly but i think it was laying in the bottom of the hole under a piece that was in there and it should of been on top of it.I switch it to where i thought it should go and it works perfect now.I never could stand the AC not blowing at me,it would take awhile for the whole car to cool down with it blowing out the defrost and floor.

 

[pwrplygoal99]

Thanks Mike I will check it out today

 

[hesermon]

Here's a link. Looks complicated but it's really pretty simple. Start at the vacuum block follow the black hose to the vacuum ball or tank. From there you should have a purple hard line (#3) going down between the inner finder and AC box to a grommet that passes through to the inside of the car. The Grey hardline (#1) comes back from the cabin to the heater control valve. If all these are intact, then use the diagram to follow lines to each of the inside components. I've found that most problems are either under the hood on the hard lines or at the grommet where they pass through to the cabin. I can also share a trick with you for running new hard lines through to the cabin if you need to.

http://www.vortexbuicks-etc.com/AC_Heater_Vacuum_Lines.htm

 

[83ttypecooled]

vacuum

Hi,
The most common failures with our cars regarding HVAC vacuum issues are source,which is at the top of the throttle body,and the check valve,on the right rear side of the engine compartment. You could pull the HVAC control head out of the dash,and I'll bet no vacuum is present.The diagram that was provided is good, but not color coded.I think it would be prudent to look closely under the hood to make sure that the items I have mentioned are in good condition. Generally,a source issue or a bad check valve will fix this issue. Good luck with the problem!

 

[pwrplygoal99]

Vaccum

Thanks Guys for the help, so far I havent been able to correct the problem.
I looked under the hood and found the check valve u mentioned it was in bad shape (cracked), I replaced it hoping it was that easy, but it didnt correct the issue, I then pulled the control unit out of the dash, I DO have vaccum on the purple line coming into the unit.

I was told by a mechanic it could be the Vaccum selector switch on the back of the unit where the hoses connect, apparently there is a diaphram in it that can go bad? I ordered one today $16

Any other suggestions would be great.

 

[83ttypecooled]

Hi,
Good to hear you have vacuum to the control head. I was wrong on this one! That means you have a major leak in some other area of the vacuum circuit. Are you running a healthy cam? If so, it can only give you 8 or 10 inches of vacuum at idle. I can't think of a lot of other reasons,besides the vac switch,that would cause this. You should be able to hear a hiss if there is a leak inside the car.