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Old 08-25-2004, 12:36 PM
jcyuhn jcyuhn is offline
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Join Date: Jun 2000
Location: Plano, TX
Posts: 2,574
Steve -

Have been too busy to respond of late, apologies for the delay.

I believe your ice cube bypass is improperly wired. Arthur has identified the correct solution in his text, but the instructions he has quoted from a previous post apply to a gasser; diesels, for some mysterious reason only understood in Stuttgart, operate differently. I have successfully built and used an ice-cube bypass for my '87 diesel, though it has been a few years.

In general, a gasoline 124 sends +12v to pin 10 of the Klima as the signal to operate the compressor. Your diesel grounds pin 10 of the Klima socket to signal operation of the compressor. Use your DVM to check voltage between pin 5 & 10 with the a/c switched off, then on. I expect you to see indeterminate voltage during the first test, and a solid 12v on the second.

If so, modify your ice cube bypass as follows: pins 85 & 86 (the relay coil) connect to pins 5 (+12v) & 10 (PBC ground signal) on the Klima socket. Not sure if it matters which Klima pins are connected to which relay pins. If it doesn't work, try swapping pins 85 & 86 on the relay - some relays are sensitive to the direction of current flow.

Pin 30 on the relay is also connected to pin 5 (+12v) on the Klima socket. Pin 87 on the relay is connected to pin 7 (compressor coil) on the Klima socket. Pin 87a on the relay is unused.

So if it is all working correctly, when you push the a/c button in the cabin, the PBC grounds pin 10 of the Klima socket. Since pin 85 of the relay is now grounded, and pin 86 is connected to 12v, the relay activates. This connects 12v at pin 30 of the relay to pin 87 of the relay, which then sends +12v to the compressor clutch. The compressor switches on, you get cold air and a smile on your face.

A couple of notes on the bypass circuit. You will of course lose the RPM comparison compressor cutout circuit. Whether this is a bug or a feature I will let you decide. Having had a compressor seize up while crossing the west Texas desert, I rather like it.

You will lose the high temp cutout circuit. The Klima relay shuts off the compressor when engine coolant reaches 115C degrees. Of course, you can monitor the coolant temp and take care of this manually. Shouldn't ever happen in a properly operating car.

You will lose the full throttle compressor cutout. So you stay cool while passing, but it takes longer to pass. You can always switch to E/C before accelerating around slower cars.

Finally, the transmission kickdown will be disabled. At higher speeds the car will no longer drop into 3rd gear when full throttle is applied. You'll notice the Klima relay is actually labeled "Klima+Kickdown."

I ran the ice cube bypass for a few months, but decided to replace it with a fresh Klima once things were sorted. I had multiple problems triggering the compressor cutout: excessive air gap on the compressor clutch (due to normal wear), plus grease and oil on the compressor clutch surfaces. These two problems caused enough slippage to trigger the cutout circuit on the Klima relay. After fixing these issues, I reinstalled the original Klima. The compressor no longer cutout, but would switch on & off in a rapid, random succession. I ordered a new Klima relay, and all has been well since. I think all that diagnosis and work was in the summer of 2000; not exactly sure.

Guess my point is this: Klima relays do go bad. They do more than just switch on the compressor, so I see the ice-cube bypass as a temporary/diagnostic fix.

My $.03 (long post...)

- JimY

quick edit: Here's a link to a site with ice cube schematic & explanation: http://www.teamrocs.com/technical/pages/relay_basics.htm
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