StratfordShark

Been having some fun today testing the vac lines from the HVAC manifold in the centre console. Mity-vac is mighty useful.

It's very tricky getting the middle screw of the manifold off so I've just been cutting and re-splicing the lines as they exit the manifold.

The (white) heater control valve is fine for vacuum (I know the actual valve may be warped but the current project is to fix the vacuum leak) but I was able to test this directly at the actuator itself.

Yellow (footwell) holds vac.

Orange (centre comb flap) leaks badly.

I haven't tested the blue (recirc) or green (defrost) lines yet but I'm really hoping they're OK. I've also had an idea that I can check for no other leaks by plugging the orange line at the manifold, then seeing if the black line at the 4-way holds vacuum with power on and testing the HVAC controls. If the blue and green are both fine then it should hold vacuum so I only need to cut them if I still have a leak.

The centre actuator attachment looks a little tricky to remove/re-attach (have read lots of posts referring to broken actuator tabs, and doing keyhole surgery via the glovebox air port) and so far I haven't had to remove the centre console, just the two carpeted sides. Have also read John Pirtle's write-up though mine is RHD.

My question (at last!) is what would be the effect on the HVAC functionality if I just plug the orange comb line for now and button things up, assuming all the other lines are holding vac OK? Also any tips for the best way of replacing the centre comb actuator, or at least just the diaphragm part, and re-attaching to the flap given that I have a RHD S4?

Thanks in advance,

Adrian

rcoble

the comb flap just forces a little more air through the door vents. No problem plugging the line.

StratfordShark

Thanks - that's excellent news especially if the recirc and defrost actuators turn out OK. Too dark to do any more work now (shark is outside awaiting new plug leads which is why I embraked on the vac leak hunt) so will get back in there tomorrow.

If this fixes the vac problem then I should get my flappy valve operational again - looking forward to seeing the effect on upper revs performance.

Best,

Adrian

IcemanG17

I plugged my center flap too.....all it really does is direct additional air away from the center vent to the side or defrost vents.....the default (failure) mode is to direct air away from the center vent...but mine gets really good airflow even with it "broken"....so I just capped it & everything else works great...

Another thought....the defroster is probably fine...but check the blue-reciculation flap....typically it leaks too (mine does)

StratfordShark

Another thought....the defroster is probabaly fine...but check the blue-recriculation flap....typically it leaks too (mine does)[/QUOTE]


Thanks for the info Brian. I will check the blue recirc line as well before I button things down.

Is your recirculation line plugged as well as the centre vent line? I understand that a leak in any line destroys the vacuum in the others (and the flappy valve line to solenoid).

Best,

Adrian

WallyP

Adrian,

If you will send me a standard email (not on this Forum) and ask, I will send you a paper that I wrote on the 928 HVAC system that should help you. The email address is
techAT928gt.com

Change the AT to @ - just trying to keep the spam to a minimum.

IcemanG17

Adrian
I actually cut the line just after the solenoid & but a little cap on it. Really easy actually.... simple but fixed the leak!