Dark Blue

What's going on - my usualy very reliable 89 S4 just started making a loud intermittant clicking noise that seems to be coming from area behind the central HVAC vents. It usually starts under acceleration and lasts a few seconds. Before I tear into the dash, is this the comb flap or other well known failure. What should I check first. Thanks for any tips.

Steve
89 S4 Auto

nicobel

If the click comes after you turn off the AC, you know the drill... there's a procedure somewhere in this forum.

jeff jackson

OR...if it comes immediately after you turn ON the AC...its probably the miniature relay in the AC Control head, that is meant to engage the compressor clutch. It has insufficient (undersized) for the current load required by design...and also isn't provided enough operating current by the harness wire sizing. So this problem is inevitible. The relay "Chatters" in retaliation to its load and lack of sufficient current to keep its coil "pulled in". Numerous remedies are avaiable to this problem.

heinrich

tapping behind the upper grille is the comb flap actuator. clicking behind the ac control head it may be the relay in the actuator. down low it may be one of the vacuum relays. You can test all of them by using different settings for the climate control.

Dark Blue

Heinrich and Jeff, thanks. I found the excellent write-ups on checking and repairing the comb flap actuator. Before I dig into the console, what should I do to isolate whether it's the relay or flap actuator (settings, etc.). I greatly appreciate your help. That comb flap actuator R&R looks like a PITA. Thanks.

Steve
'89 S4 Auto

ODSharkBytes

Just throw some nuts back there, the squirrel is hungry

jeff jackson

Like I said, if the chattering "starts" when you turn ON the AC button...its a good possibility its the controllers internal relay to pull in the AC clutch coil. The comb flap actuator can chatter, when the HVAC controller is changed through its various control programs. These are the settings of the lower lever on the HVAC control head. And the chattering will happen regardless of the engagement of the AC pushbutton switch.

deliriousga

My clicking sound was just a vacuum leak. The recirculation flap was making the noise behind the center vents. I replaced the check valve and 4-way vacuum connector under the hood (next to the brake fluid reservoir) and everything has been great since. You can also check the vacuum connections that are under the center console in the front by taking off the driver's side panel that goes under th dash. Those are two easy things before taking the console out if you're not sure what is causing it.

Good luck!

gamut200

Resurrecting this thread again with the hope of resolving the exact same issue “deliriousga” had. I have the same clicking sound behind the dash only when the engine is under load or acceleration. There are no sounds / issues when I use the HVAC. I replaced the check valve with no difference and will try the 4 way connector next if I can get hold of one. Any further help on how to find this (assume vacuum leak) will be much appreciated. Car is a 1991 GT. Thanks!

Mrmerlin

go to 928GT.com and look for the Wally HVAC system you will need to remove the console to get to the required parts.

The 928 Hvac System - 928gt.com

mkhargrove

the ac controller housing might be broken so that the top and bottom piece aren't fastened together, which allows the sliders to have wonky contact and will cause a lot of random things to happen

Guy

I have had this issue on three early cars. In each case, the problem was one of the vacuum solenoids behind the ac controller. I added a second ground to the vacuum block and never had an issue again.