928S4 HVAC Controls Question
 

Hello everyone and thanks for your input in advance. I am hopefully ironing out the last few details (ha ha) on my 1987 S4 that "everything worked" when I bought it.

Needless to say it's been a LONG, mutli-year journey to get the "everything working" part working.

I am to the point of actually driving the car and working on the climate controls. Here is my problem:

If you switch the manual HVAC slide lever to anything other than full left - "off," the heater control valve looses vacuum and opens up giving me heat. Fine for the winter, but not summer. Regardless of the a/c switch position (a/c compressor shot - that's next) the valve opens. The rest of the position switches (i.e. defrost, front vents, and footwell vents) all work according to the position selection as they should.

I tried the temp lever switch all the way to the cool side too. Is there a vacuum circuit between the upper and lower slide levers (temp vs. vent selection) I need to look at?

Looking for guidance on where to start.

Thanks again,

Bob

Heater Control Valve -
 

Hey Fischer - It sounds like you have an open vacuum line connected to your "Heater Shut Off Valve". If the vacuum source to this valve is lost - it's spring loaded to fall open and let hot water continuously through to the heater core. Here is a write-up on how to Troubleshoot the 5 vacuum solenoids used to control all the HVAC flaps, doors and valves.

https://members.rennlist.com/pirtle/svc_act.html

Just about every owner has had to chase down a vacuum leak or two in the HVAC temp control lines.

Good Luck - Michael

Michael- thanks for the link. It gives me direction. I will post a follow up when I can. The heater control valve closes when you slide the lever to off, but every other position it just opens. I’m sure there are other lines somewhere inside the dash that are disconnected. I’ve replaced every vacuum line under the hood and rebuilt the whole intake system. The lines were a mess of disconnected lines and I wonder how the car ever ran to begin with.

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So, it's a nice day to work comfortably out in the garage. I pulled apart the dash to get at the solenoid valves, HVAC controls and beyond. Thanks to Michael I honed in on what I think is the problem..

When the car is running, and all the heat/air is off, I have a good vacuum that keeps the heater control valve off - about 15 inches on my mity-vac at the 5 solenoid control cluster. As soon as you select any direction of airflow (defrost, foot, center vent, etc) the vacuum drops down to roughly 5 inches, which is what must cause my heater control valve to open as that isn't enough suction. I checked the operation of each solenoid valve with a volt meter versus if it was open/closed. They checked out. I traced down to leaking actuators: One for the footwell flap (yellow vacuum line) and one for the recirc flap (blue line). Both have a slow leak.

I could easily access the footwell flap actuator and took it apart and found the pin hole as pictured above. I'm at a loss as to where the recirc actuator is located so any hints would be appreciated :)

I also took apart the electronic control unit and cleaned all the contacts and connections since I was in there already...

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Thanks for the help so far!
Bob

Fischer, the recirc/fresh air actuator is located above the Central Fuse panel. It is bolted in/screwed in and glued in. Be patient when removing it.

There are 3 screws that hold the blower motor in the cowling area. 2 from above and 1 long phillip's head screw that is accessed in the passenger footwell above the Central Fuse panel from underneath and located in the middle of the grill area of the actuator box.

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Oh boy - That recirc assembly was not fun. I eventually removed the whole assembly and motor thanks you guys and a write up on Rennlist by John Pirtle.

Basically there are 5 vacuum actuators and 4 of them were leaking.

1. My heater control valve was the original leaker which I had replaced when I re-did everything under the hood.
2. The comb flap center console actuator is leaking
3. The recirc actuator which we talked about
4. the footwell flap actuator mentioned in a previous post.

Amazingly, the defrost actuator behind the gauge cluster is not leaking today, but will probably give out when I get my car all back together.

The vacuum line to the recirc actuator was leaking too and cut under the plastic cover under the hood. Why? - Just because. So I replaced the entire length by using a cut off nail and some heat shrink tubing to splice on a new line to the old, and pulling it through. Thank God that held and worked!

So I have a new actuator for the footwell flap on order that also fits a BMW and a Mercedes E class of the same vintage. It was $38 shipped.

The recirc actuator is quite beefy, and the comb flap actuator is a mystery as to how to disconnect that with orthoscopic surgery tools?


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This is looking through the duct hole after removing the tubing at the comb flap actuator attachment. It is far back in there and my phone makes it look easier than it is. Any suggestions on this one?


Lastly, as I had the whole blower assembly out, I took apart the motor and have left the bearings soak in some T5 light oil/lube as one of the bearings (most likely the lower one) squals on initial spin up. Anyone here have success on replacing the bearings in here?

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Replace the defrost actuator WYAIT. It will wait until you get everything back together to start leaking otherwise.

If we told you how to replace the comb flap actuator without orthopedic tools, we would have to kill you.

Since you have the blower motor out, this is a great time to replace the motor with an upgraded resourced higher output motor that will actually blow your hair back when switched to high speed. Ask Roger for the replacement.

Alright John - I know for a fact one 928 enthusiast would not kill another. There's already a shortage of sick & twisted individuals who put up with and maintain these cars!

I don't need any more airflow, and I see a new motor is about $200. I might take it to my local motor rebuilder and see if he can just swap out the bearings for a few bucks or I might try and take a crack at it myself. There's lots of bearing places around here. I've got nothing to lose if I have to end up buying a new one anyway.

I guess I should have put the smiley face after the snarky comment. Here it is: :)

If you have long handled needle nose, you can reach in the hole that you took the picture from and gently squeeze the plastic that holds the metal arm on while removing the metal arm. When I did this, I apparently was too ham-fisted and broke the plastic, but I got it removed. Upon reinstallation, I put a small amount of JB weld on a stick and rebuilt the plastic to hold the metal arm on again. I think if I was to do it again, I'd use a round piece of plastic bigger than the hole and use JB weld as strictly a glue to stick the round piece to the remaining plastic.

Good Luck!

Guess it’s time to break out the video boroscope and the long needle nose then. Maybe this weekend I get another attempt at it. I’m waiting for several versions of vacuum actuators to be delivered. Whoever buys my car when I’m done is going to get all the heavy duty repairs out of the way thanks to me....

Turns out the motor doesn’t use ball bearings, just a bushing. I carefully pried open the top of the motor, sanded smoothe the corrosion on the motor shaft, greased it up, and reassembled the motor. I also sealed up where I pried it apart with a touch of JB Weld to ensure it stays put. Motor runs quiet when hooked to my battery charger.

Waiting on two more vacuum actuators....

Blower Motor Brush Check -
 

Hey Fischer - While you have the blower motor out - you might inspect the commutator surface for wear and check your brush length. Our blower motors accumulate a lot of mileage since they are set to run most of the time. Gently clean out the mica insulation spacers between the commutator segment bars with the blunt side of an Exacto-knife. An eraser works great to clean and smooth the commutator surface, then blow everything out with compressed air.

Both a couple of buddies along with my own blower motor commutator were found to be in good shape, but our brushes were all pretty worn. Since I couldn't locate a replacement brush set, I decided to make some. A pair of starter armature brushes from an automotive starter/alternator supply shop had the basic materials for $2. The loop of copper wire attached at one end of each starter brush was 1st cut in the center. The starter brushes were then sawed length wise down the middle using a hack saw blade. This made some slightly over sized blower motor replacement brushes - each with an electrical "Pig-Tail" as seen in the photo.....

The old brushes are removed by gently bending the folded over tabs at the top of each brush box. I now cut the electrical leads off each worn blower motor brush "Flush" with their top surface. The old brush "Pig-Tails" that remained on the blower motor winding side provided an easily accessible electrical attachment point for each of the new brush "Pig-Tails".

With the width and thickness of a worn brush as a guide - I sized the new brushes using a medium flat file until each one would slid through the blower motor brush box. A table mounted grinding wheel helped to match the curved contour of each new brush face properly sit against the blower motor commutator surface. With the new brushes installed, each (Old/New) pair of "Pig Tail" leads were joined together. I 1st crimped the leads together using a shortened electrical splice - then soldered each connection for good measure.

After a few test runs using a spare battery - the lower photo flash doesn't indicate the smooth commutator surface very well but it does show the top of the brush box - brush spring installed and securing tabs folded over. The brushes quickly seated themselves and my blower motor has been running like new for several years.

Good Luck - Michael
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Awesome write up Michael. I did take a look at the brushes and had about half left. I figured that took 32 years to get there, and at the rate I’m driving this car versus wrenching on it they should last another 1,325 years, give or takehttp://forums.pelicanparts.com/suppo...s/a_frusty.gif.

I just reinstalled the recirculating assembly and I am in process of putting the fuse panel back in and tidying that up. I still have two more vacuum actuators coming tomorrow for the footwell and the dreaded center comb flaps.

I fixed so many fluid and vacuum leaks under the hood and now so many under the dash I don’t know how my car ever ran in the first place.

Update- replaced all the vacuum actuators. Bought some German Behr actuators for $23 (on sale) each and carefully drilled out the rivit holding the generic metal arm. Then I simply installed the old Porsche metal arm on with a new rivit.

The comb flap actuator was not fun, nor was the recirc flap actuator. On the comb flap, I was able to reuse the housing of the old one as suggested on here to save my sanity of somehow re-attaching the base with the press washers. It took what seemed like a half hour of looking through my video boroscope and using a socket extension to press on the arm to the plastic bushing. I also laughed at myself a few times realizing I would make a terrible micro-surgeon as I was clumsily was banging around in there.

I now have 20 inches of vacuum at idle and all the actuators actually work really fast. The heater can actually turn off when commanded and does not come on when selecting cool. I now need to replace the a/c compressor and get it cooling! That should be easy compared to all the above work... I hope 🤞

Another question - What is this hose doing and does it connect to something?

Just ordered a new compressor. I hope this goes easy compared to the actuators. I am in the biz, so I have all the tools at least! The compressor is practically handed to you under the car. Mine comes on, but builds no pressure. System is leak free though, which is a HUGE plus.

No hose picture attached

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A rookie mistake! Don't know what happened to the first one I attached. Maybe I didn't wait long enough for it to upload. My bad.

Glove box cooling tube, I believe. It plugs into the glove box to keep your ice cream nice and cool on the drive home from the market. :)

a/c evaporator drain? - maybe? - if it is you're missing something to get it to exit the car

I was hoping that was it. It didn’t seem right to be a drain, and I was hoping it wasn’t because there was no exit to the outside. However, I didn’t really see a plain as day spot in the back of the glove box either.

Just got a new compressor delivered, just waiting on the oil. I drove it today with a bit of heat on and the sunroof open. It seems like forever since I drove it. I forgot that I could. I’m so used to it being in pieces as I’ve tackled lots of major maintenance items that crop up on a 32 year old car that had been sitting for six years....