My tale of the HVAC system causing starting issues

[Steve Brookes]

Some of you that came to the Curborough bash will know that my car developed an issue with the immobiliser locking on and preventing me from firing up the engine. It was one of those frustrating intermittent electrical faults with no clear path to investigate. I could get the immobiliser to unlock by randomly pressing the fob. There were times when I would think that's it, it will never come off and all of sudden it did! Putting it into a garage didn't seem like the right approach because the random events were never reproducible. I'd already put a new battery on so that eliminated a bad battery from being the problem.

Luckily, on the way back from Curborough fuse #1 blew and while this meant I had no control of the HVAC system, the problems with the immobiliser ceased. I could get it to unlock and start the car every time. If I put a new 25 amp fuse in position 1, the random immobiliser problems came back. Therefore I now knew that I had to find the fault in the HVAC system that was interfering with the immobiliser. I'm not very knowledgeable of electrics but my thought process was that the HVAC system was causing a big current drain as soon as the ignition was turned on.

My first thought was that the blower motor had siezed but taking it off showed that it still turned freely. So then I suspected a siezed front cabin fan. I unplugged each but they had no effect on the immobiliser. I then looked at the final stage regulator (FSR). Here it is plugged in:

So I unplugged it:

The problem with the immobiliser disappeared. It would unlock everytime so I could start the car. With the problem solved I snapped up a used FSR that was on 'buy it now' on ebay and headed off to my trackday with the old one still unplugged. This meant that I only had the slow flow of the rear blower for de-misting so I had to open the window to stop the car steaming up. After an hour so the problem returned so it wasn't the FSR after all! Should have done a test drive and not just tested the effect on my drive [].

Now the only thing left to try, was to remove the climate control unit (CCU). That was duly removed and I took the little fan off while I was at it (incase that was the problem with the CCU which I could try later):

While removing the CCU I found the famous 'green radio wire' that is known to cause current drain if it earths on the body. It looked to be pretty well insulated but I taped it up more for good measure (it's not used on my Alpine head unit):

Tests on the drive indicated that with the CCU removed the immobiliser problem was solved []. So I went for a long test drive this time. It was bloomin' cold without any heat and the window down to stop the screen misting up. However, this didn't solve the problem either as the stuck immobilser came back when I stopped. [&o]

So at this stage I was still left at the point where with fuse #1 out, all was fine but none of the main HVAC components seem to be at fault. i.e. with fuse #1 in and one of the HVAC components disconnected, the immobiliser problem was still there. Finally, and although I'd not noticed any problems with the rear blower not running, I pulled the rear blower relay (audi part shown in the pic below):

Not only did that solve my immobiliser problem but replacing it with the oil cooler relay (identical part) meant that could have both the HVAC system working and a car that starts! Now just need to go and get a new relay to put in the oil cooler slot []. In fact, I'll get two new ones while I'm at it []

 

[iangray100]

Thanks for the update...I think I will replace mine [8|]..not that i have but its the 2nd issue I have heard with this relay issue this week . Today I just changed the iginition key electrics due to others having known issues ..i'm glad i did as it was going to fail very shortly as it was all falling apart inside...replacement was only £39 off OPC but it could be seen as a little fiddle to fit to fit with the barrel still in the car (as you need a specially thin screw driver 90% racket to get the top screw out with the ignition barrel still fitted ..luckily i purchased a set on my USA travel years ago ;-)

 

[vitesse]

Steve,
Many congratulations on solving the riddle-so the moral is-before stripping anything down-check not only the fuses but also the relay(s).Whilst I have electrical test stuff like a continuity tester which includes a test neon & bleeper, the more simple version with just a lamp,amultimeter & also a dedicated car electrics tester which can check batteries,dynamo & alternators, resistance,& dwell meter(can you remember contact points),I have never assessed how to actually test relays nor the symptoms which faulty relays impart into the electrical systems of cars like the 964 other than the standard procedure of swapping a like relay.
I think there was a mention in a post very recently of building a test board-sounds like a good subject for PP-I wonder if Bosch or Hella do something?

On my alarm problem,have had no repeat since switching the ultrasonics out-I also haven't proved that that was the cause nor checked out any components-what I have done is restored the full key central locking by copying the recent post involving removing the knob,bezel & spraying the locking mechanism through the door card opening thus revealed with a heady mix of WD 40/teflon spray.Initially not much difference,but a spirited drive for 4/5 miles roundabout Formby allowed the lubricants to do their work & now everything is working properly-I did think this could possibly affect the alarm.

 

[Dave Wilkinson]

Glad you got to the bottom of it Steve. You could have used the a/c blower relay (R14) as a stand-in to save risking your oil cooler. From what I've heard I think these relays tend to suffer with welded contacts so at some point, when they operate, the current carrying contacts weld themselves together and effectively hold the relay in the operated condition, even when the CCU has released it. I'm guessing that's what creates the current drain.

Regards

Dave

 

[Steve Brookes]

Some good points there gents.

Although in hindsight just swapping relays would have been the answer it's worth noting that in my case I hadn't noticed a problem with the HVAC operation prior to the darn car having immobiliser issues. Blowing fuse #1 with the result that the immobiliser problem disappeared, indicated that the problem lay with the cabin side of the HVAC system hence it was that part that I decided to work through first (that's probably a result of me being a scientist too long and always trying to be methodical in my problem solving). If the rear blower fuse had blown I would have started there instead. I should say at this stage that I received a lot of help from Dave by e-mail and neither of us could see a clear path to solving the problem.

The problem was compounded by it being intermittent and random. In hindsight I can say that the only times I didn't get problems with the immobiliser was when I first started the car when it had been left overnight. The blower relay is in what I term a 'failing mode'. It's when it's warmed up a bit that it causes problems with the immobiliser. I did in fact inspect the relay early on but it threw me a red herring because side by side with the oil cooler relay it looks newer because there is less discolouration of the letters on the casing.

I'm glad I worked through it all and re-learned the value of test driving because without doing that I could have gone to the expense of replacing the CCU (£1,000+) or sending it off for repair (£250ish). All for no result! I wasted £50 on the replacement final stage relay but that will go into my ever growing cupboard of 964 spares. I can also make it available to forum members on a sale or return basis for anyone that has a problem with their's (can be quite common I believe). BTW the bolt by the petrol tank makes them a PIA to swap out!

I didn't use the aircon relay (R14) for the swap because my aircon has not worked from day 1 so I had no confidence in it.

And thanks for pointing out that ignition switch might be another one to add to my list! []

 

[Steve Brookes]

Oh yes, I just remembered that I have a question as a result of my diagnostics.

I noticed that when my immobiliser disarms successfully that I could hear a definite click from the engine bay. When I handed ignition controls over to the Mrs and listened in the engine bay, the click (more like a clack actually) came from around the ISV area (or maybe the AFM). Anyone know what that noise is?

I should say that mine is a remote immboliser and I disarm when I have already turned the key so that all lights are on the dash. Those that disarm their immoboliser before putting the key in the dash might get the same noise when they turn the ignition key to all lights on.

 

[Dave Wilkinson]

Steve,

I'm guessing that the noise you hear is, indeed, the ISV. When the immobilisor disarms I'm guessing that it applies power to the relevant circuit to power the fuel pump and the DME. Once the DME gets power it will activate the ISV (as long as the throttle is closed) and I reckon the noise you hear is the initial movement of the ISV slide.

Being an aftermarket imobilisor it may not be everyone's experience since the wiring may vary from installation to installation. Some immobilisors, for example, may be wired to simply disable the fuel pump whereas others may do more. Without investigating the eact wiring it's difficult to say.

Regards

Dave

 

[l.chadburn]

Hi
Can I ask about the famous green wire shown in your picture. My car has a wire very similar to this behind the sterio but without the white plastic connector. Do I need to do anything with it (somehow connect it to my new sterio) or should I just tape it up. I was going to get an auto electrican to look at it but this could save me some money.

cheers lee

 

[Steve Brookes]

Lee, the general consensus is that the green wire is of only use for the original radio and that you should tape it up when you have a later stereo, to stop it draining your battery.

 

[Steve Brookes]

Sadly I have to say that this thread is far from finished. On the very next drive today the problem of the immobiliser sticking on came back! No problems starting from cold. Stopped 1 mile down the road for petrol and had a b*gger of a time re-starting it. So I then completely removed the rear blower relay, ran without and the problems of no starting persisted. Something is causing a big draw on the battery but it's nothing I've checked out so far. I also don't think it's charging properly. Looks like I need to go and buy a multimeter and learn how to use it. With luck I'll short something out and blow the damn car up! []

I don't know whether it's relevent but all these troubles coincided with my radio suddenly developing reception problems. Crackles like hell for the first few miles of a drive and then starts to get slightly better. From this I'm thinking the battery is going pretty flat when the car is first started and using lots of power for the demister fans, etc and gets a bit of charge by the time the car warms up.

Things I'm leaning towards are:

* Alternator is on its way out or the belt at least needs tightening
* The clock is causing the drain (I've heard of the clock causing lots of issues)
* The ISV is sticking and is difficult to move on a low battery (see above about the immobiliser operating the ISV)
* I don't get the clink of the flappers when shutting the door and wondering if sticking flaps could cause a current drain. However I still get heat in the cabin and I've never heard them clink since I got the car.
*Have the immobiliser ripped out (but I think that would just be removing a symptom).

What with these electrical gremlins and a big water leak that the boot has developed...I'm not best friends with this car at the moment! [][][]

 

[kevin]

Crackling on the radio?, I'd go for the alternator, the brushes don't last forever, I think I got a pack a while ago from Ollie for about 25 as an insurance policy, my car had done 105k, and they were pretty well worn.

kevin.

 

[Dave Wilkinson]

Steve,

I'm trying to follow this epic but it seems to be getting more confusing as time goes on!!

Regarding the "clink" of the flappers, there is no liklihood of them being the source of the current drain since they are purely mechanical. You don't always hear the "clink" because it depends on how you leave your heater controls. If you leave the temp control on the blue dot when you park you will never hear the "clink" because the servo-operated flaps into the mixing chamber will be closed and there is no open air path from the cabin to the flapper valves. If the temp selector is NOT on the blue dot, the mixing chamber flaps will be open and allow the compressed air from the cabin created when you close the door to vent through the mixing chamber, down the sill tubes and momentarily operate the flapper valve - hence the "clink".

I have my doubts about the clock causing the current drain but it's worth checking when your charge light goes out. The clock connections are renowned for causing a problem where the charge light won't go out until the engine is rev'ed to about 3000 rpm. If this happens there is a chance your battery isn't getting refreshed quick enough after a start.

The sticky ISV has some potential but it might just be that it's an effect of the problem rather than the cause. It might be worth taking some voltage measurements of the battery before you try to start the engine. That might give a clue as to when the problem may or may not appear.

Kevin's note about the alternator brushes is worth checking out but your previous efforts to trace this seem to suggest is more of a drain issue than a charging issue. Checking the battery voltage over time might be a way to convince yourself.

Good luck with the on-going search.

Regards

Dave

 

[Steve Brookes]

So between yesterday and today:

Took the clock out and drove around with it missing from the dash. This had no effect on the problem so that is ruled out.

Disconnected in turn; the plenum temp sensor, the blower balast resistor, the ISV. None of them had any effect on the problem.

Measured the battery voltage: 12.5 volts with every thing off and 13.8 volts with the engine idling. That says to me the battery is good and charging pretty well.

The only thing that removes the problem is pulling fuse #1. With that out it starts every time without fail and there's no crackling from the radio with the engine on. This is why I keep coming back to the problem being related to the HVAC system.

Maybe it's a stuck servo that is pulling too much current? Is there a way to unplug those individually.

And regarding the flapper clink, I get nothing regardless of where I move the the temperature sensor to. I guess I need to investigate these anyway.

 

[Dave Wilkinson]

Steve,

Eash of the servos have their own 5-pin connector but getting to it may be a challenge!! Roly Baldwin's write-up on John's site (http://www.porsche964.co.uk/technical/servos.htm) is worthwhile looking at.

Regards

Dave

 

[iangray100]

Guys FYI,

Ref Steves relay issue. I checked inside my relays today to see the status of the point connectors inside the relay covers, as you can flip the relay covers off quite easily to see the solenoid connections.

Interesting the double relay in the left-hand engine bay had a a lot of evidence of sparking and was showing pretty worn points connections..which is why Steve's burnt closed I suspect .
I replaced this one with a new one, I then checked the same type of, double relays in the front fuse/relay box and both of these were showing heavy signs of worn relay connections points. I also checked inside the other remaining relays and these obviously switch far lower currents and were A1 on the point connection.

So the out come this investigation is after 17years these high current relays ( three in total in the car) are showing there age..so I will be replacing them to eliminate any pending issues that have shown up on the forums. Interestingly Porsche UK @ Reading have them in stock !! Part no: 811951 253 Approx £25 each

 

[Steve Brookes]

ORIGINAL: Dave Wilkinson

Steve,

Eash of the servos have their own 5-pin connector but getting to it may be a challenge!! Roly Baldwin's write-up on John's site (http://www.porsche964.co.uk/technical/servos.htm) is worthwhile looking at.

Regards

Dave

Thanks for the link Dave. I'd forgotten about Roly's excellent write up. Hopefully I'll be able to start checking out the servos at the weekend. As I can direct flow between the screen and footwells and adjust the temperature, I guess they're all working but maybe one or more are pulling excessive current.

Regarding the flapper valves, you say they are just mechanical. Can you describe how they work as part of the HVAC system? I'm going to examine these too. I've found some threads on Rennlist that tell about freeing them up by tapping them with a piece of wood and then lubricating with WD40. But no doubt I'm going to have an argument with rusty jubilee clips first! []

 

[Dave Wilkinson]

Steve,

The flapper valves are simply a means of routing the hot air from the heat exchangers to EITHER the HVAC mixing chamber OR the dump vents in the rear wheel wells. They work on simple air pressure so the moving part needs to be reasonably free to move within the housing. The hot air from the heat exchangers is delivered to the input of the flappers under a slightly raised pressure, created by the main alternator fan or (generally) the rear blower.

If the mixing chamber servos have the entrance to the mixing chamber closed (i.e. no heat required) there is a tendency for the air between the flapper valve and the mixing chamber to rise in pressure ('coz there's nowhere for it to go) and that causes the flapper valve to be resistant to moving, hence leaving the vent to the wheel wells open.

If the mixing chamber servos open the mixing chamber, the air pressure in that link will drop (since the air can now escape into the mixing chamber) and the flapper valve will flip to close the vent to the wheel wells and open the route to the mixing chamber. Hence, you get heat.

As I mentioned before, if the temperature selector is left off the blue dot when parked, the air path through the mixing chamber is open all the way to the flapper valves, so closing the door creates a pressure wave in the cabin which then travels down the sill tubes via the mixing chamber and momentarily "flips" the flapper valve - hence the metallic "clink" that many complain about.

This is one of those situations where a picture would be worth a thousand words, but I don't have a picture I'm afraid!!

Regards

Dave

 

[iangray100]

See my link Steve, I took them all apart when I had the engine out as my flaps were solid.

http://forums.pelicanparts.com/911-engine-rebuilding-forum/340187-964-3-6-full-engine-rebuild-over-uk-2.html

or http://forums.pelicanparts.com/showthread.php?t=340187 ..on page 2 half way down

I then just drilled the flap pivots out a little and screwed them back up ....they work a treat now ( the actual pivots cups for the flaps are plastic/nylon and become tight with age and heat, so WD40 wont help realy )

 

[Steve Brookes]

Thanks for the description Dave and thanks for the pics Ian - paints a thousand words as Dave said []. Hearing this from you guys makes me wonder that if the flaps aren't moving freely whether this could put a strain on the mixing chamber servos which eventually leads to them failing. Or in my case the servos drawing too much current.

There's another picture here of the flappers:

http://forums.rennlist.com/rennforums/964-forum/493077-heating-system-flapper-valves.html?highlight=flapper

This thread about the flapper valves and mixing chambers also has some nice pics. And there seems to be a constant theme of the servos that go bad are #2 an #4 which control the mixing chambers on each side. And of course each of these is linked to a flapper valve.

http://forums.rennlist.com/rennforums/964-forum/209129-differential-pressure-flapper-valve-question.html?highlight=flapper

Out of interest Ian...do your flappers have a plastic bend between the metal housing and the heat exchanger hose? PET shows this but my hoses are just joined directly to the metal housing which looks very awkward.

 

[iangray100]

The flexy pipe connects to the flapper housing and heat exchangers and is J-clipped at each end . As you say they will be rusty and I doubt you can get them off cleanly . PS: the flexy pipe from OPC is silly money . Berts are far cheaper and OPC supplied the clips. PET I'm sure is not correct as it shows an elbow .