My tale of the HVAC system causing starting issues

[iangray100]

Oh...as an extra I also blocked off , by cutting a SS piece of metal and fitted it under the two plastic flaps, these - other flaps are next to the seat belts hubs, as I was sick of using the sun roof and get hot air in the car from the side window inlets via from these two outlets.....more flaps !!!

 

[Steve Brookes]

ORIGINAL: 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 .

Hmm....that's very interesting about the elbows. I've always had utmost faith in PET. Makes me wonder if the elbows might have come in right at the end of the 964 line? It would be interesting to hear if anyone with a 93 car has them. And your right about the hoses....80 quid each last time I enquired!

ETA - my faith is restored in PET which only lists the elbow as being used on the right side of the turbos []

 

[Steve Brookes]

Made a small amount of progress today.

After chatting off-line with Sten I first made a few current measurements. The first measurement was made with fuse #1 removed. The car had been cooling down for about 15 minutes, all doors were shut, interior lights off, bonnet switch isolated, etc. The current was a steady 1.35 A. With fuse #1 replaced and everything the same I didn't spot the next reading because of the smoke and sparks that came off the battery lead when I tried to measure it :icon501: . At this pointed I halted any further measurements for fear of burning out some wiring.

Then I reconnected the battery to its normal state and fuse #1 blew straight away. I then disconnected the plugs from all five HVAC servos (pic of no. 5 servo unplugged below). With all of these disconnected, fuse #1 blew again!

Then I disconnected this plug that sits on the cabin fan housing on the right:

Here it is with the cap off showing all the wires that terminate inside the plug (the eagle eyed will notice that there is a green/white wire on the right that doesen't have a corresponding pin on the lower plug):

With this unplugged and fuse #1 replaced my immobilizer and starting problems disappeared. I guess I should have taken another current reading again at this point but the previous sparking had put me off doing it again. But suffice to say that the problem is gone with this connection unplugged (the problem with radio reception is also gone - see first post).

Since the cabin fans or the CCU do not work with this connection unplugged, I presume this is the main junction plug between the HVAC system that sits under the bonnet and the CCU?

Now I have the dilema of trying to work out why there is a big current draw when this connection is plugged in. My current logic is saying that there must be a short in the wiring between this plug block and where it plugs into the CCU. The reasoning behind this logic is that my immobiliser problem was still present when I had completely removed the CCU from the car. So I guess I need to examine the wiring between this plug and the plug that goes into the CCU. I'm sure this is not going to be easy!

 

[Steve Brookes]

I have all my digits crossed that I have now solved the problem. However I have to say that I'm not entirely certain how I did it [&:]. As mentioned above unplugging the terminal to the HVAC system would remove the problem of the immobiliser sticking on. So I gave it a thorough inspection and a dust down - it's in two halves so I inspected each half for possible shorts. I then reassembled and plugged it firmly back together and hey presto, there were no more problems cancelling the immobiliser.

To double check I then re-measured the current drain. Before, with fuse #1 in, the drain was so big that the positive lead and positive batter terminal smoked and sparked when I tried to measure the current. Now, I could measure it and found that I had a drain of nearly 1.4 amps. I then set about pulling the fuses one by one. When I got to fuse #11 (clock and interior lights) the drain dropped to 0.09 amps which is about where it should be. So even though the doors were shut and the interior lights were not illuminated, they were still drawing current. I clicked the lights from the courtesy position to the off position and put fuse #11 back in and re-measured the current drain. It was down to 0.11 amps. Result! (So, at some point I'll need to pull the interior lights out and sort out why they're grounding.)

For good measure I removed the earth point that the HVAC wiring grounds to inside the right front wing and cleaned the contact point and the earth wire contacts (4 of them). It was very easy to undo and the contacts were quite corroded so this might have been contributing to the problem of the high current draw of the HVAC wiring.

Also for good measure, I removed the old and very original battery earth strap. Again the contact point on the body and the earth wire connectors were corroded:

I then cleaned up the contact points and attached a new strap. You can see that Porsche have replaced the old braided style with an insulated wire. Surprisingly cheap at only £7!

Hopefully that's the end of the problem for the time being. [8|]

 

[appletonn]

Steve, great post all round with helpful pics and useful to know about those additional earth points that undoubtedly will need cleaning up on most of these 18+yr old cars by now.