Erling G-P

Thanks once more Alan,

Sounds like the 'DEF' may have been doing what it's supposed to after all. I can't say if the heat I recieved was as hot as full heat, as I've only had the car for a few summer weeks and thus haven't used the heating at all - I simply didn't expect to get hot air when the temp was set to cool and A/C running too. PO told me I had to close the center vent manually for 'DEF' to work. Tried this back when fan & A/C still worked and must admit it was the most effective defogging I've ever seen in a car !!

Just went and tried the 'DEF' setting. I can hear the flaps changing positions as I move the slider, but nothing happens when selecting 'DEF'; A/C still isn't running. When selecting 'recirc', the big cooling fans at the radiator starts churning. If I then press the A/C button, they stop again ! This seems very strange to me, since I've both read and observed myself that the fans starts up if you activate the A/C (although my own experiences are without 'recirc' selected, since this would blow the fuse as mentioned earlier)

Cheers,
Erling

UKKid35

Any chance the thread title can be edited to make it easier to find Jim's excellent AirCon relay diagnostics?

Erling G-P

Changed the title Paul as per your excellent recommendation

Cheers,
Erling

Charley B

You might find it more convenient to right click on the post # and save it to favorites. You can also rename the post appropriately and maybe start a Troubleshooting folder.

Jim M.

I wish I could take credit for "Jim's excellent AirCon relay diagonstics", but I have been coping and saving to a word document for years and years now, back to when we only had "Porschefiles." The words of wisdom are from all of you Rennlisters out there. For me it's easier, faster than trying to do a search, and is a document I can take with me when I don't have a computer. It's also saved me much time in troublshooting and unnecessary parts, as well as short cuts and alternate parts to do a repair other than my friendly Porsche dealer.

If you've done a successful repair and posted it here or on your web site, I've probably copied it and put it in my word document (now 176 pages).

Jim Mayzurk
93 GTS 5-spd

Erling G-P

Mystery solved; aircon working again. Credit goes to my (non-Porsche) workshop for finding out.

Most embarassed to report that it was just a fuse; the 30A one for the ventilation fan. Wasn't aware that this one would affect the A/C too, as all the other times the A/C didn't work, the culprit was the 7.5A fuse for the control unit.

Being new to 928s, I wasn't aware of all the things happening automatically when you select 'DEF' - I just wanted to route some air towards the windshield, to prevent it misting up during a heavy rainstorm. Didn't realise it would try to switch on my seized fan and thus blow the 30A fuse.

Very sorry to have kept a lot of very knowledgeable folks making advanced suggestions of possible reasons for non-working A/C; hope someone else can use the troubleshooting advice

Thanks again all; I'm sure my problems will become more seroius over time...

Cheers,
Erling

Alan

Per Jim's excellent notes above (that he admits to stealing with pride..!)

If anyone is worries about the AC head unit relay going bad - but it's still working for now I'd recommend a different approach as a proactive fix.

The output of the relay goes via the freeze switch through the Central Electric panel and then via the the low/high pressure switch to the AC clutch.

On the CE panel there is always at least one blank relay socket and this is a great place to mount a new relay to switch the clutch load. If the old one in the head unit works - no need to take it out (you just reduced the load on its contacts by a factor or 20 or so). Use its output to drive the coil of a new standard SPST bosch relay mounted in the CE panel.

Even if the stock relay was busted - I'd just route its coil connection to the CE panel (using the old output wire) and still put the new relay there.

The only issue is that you have to add new crimp terminals to an empty relay shell - standard 1/4" female terminals with retaining pins work (you can source Ford types).

I think this is the best solution to this issue if it happens (or if you wan't to get proactive about it).

Advantages:

Its solidly mounted - where just about all the relays are - easier to access than the console - any generic SPST relay will work (53 type) and is easily replaceable in future if needed..

- of course document the function of the updated relay on the panel with a note somehow.

Alan

VehiGAZ

I found the cause of my A/C problem, and it is the anti-freeze switch. I got 12V only on one wire, and nothing on the other. When I bridged them, the compressor kicked on and engaged the A/C. Yay!

(There were bubbles in the dryer sight glass, so I probably need a charge-up, but it's not low enough to shut off the compressor.)

Would it be OK to run the system short-term with the anti-freeze switch bypassed (with the two wires connected to each other)? If it's an actively-switching part of the system, I could understand not doing such, but if it's an emergency cut-off switch, then I would hope I could get away with it.

Jim M.

Alan, Thanks, great suggestion, even better than Dr Bob's! And yes I copied your suggestion as a future project (being proactive).

Jim Mayzurk
93 GTS 5-spd