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Idle control with A/C - howzit work?

Car is an 86 5000, serial numbers WAUFB044XGN040999, build date 9/85, has
aero headlights and non-diagnostic climate control. Not turbo (that's
important!), standard shift.

Problem is idle with A/C turned on - 600 rpm, rattle, rattle, groan. A/C
off is 1,000 rpm cold, 800 rpm hot, smooth as silk.

Checking various service docs, turning on the A/C is supposed to send a
signal to the ISV to raise the idle to 900 rpm.

Looking at schematic, both in Haynes and gen-u-wine Audi wiring diagrams,
the idle stabilisation system is either relays in positions 7, 8, 9 (lower
row, left side) OR 11-12 (one long relay, right side.) - this is the aux
relay panel inside the car on left side above package tray, which must be
removed for access.

Ain't no such animal . . .  neither setup exists on my car - the existing
relay panel doesn't even resemble the service literature (yeah, I know I
shouldn't be surprised). 

Earlier cars (85 and down) are alleged to have a wire from the climate
control head which goes directly to the ECU  (mounted behind front right
kick panel) - is this supposed to serve the same function? I suppose if I
had to I could put a voltmeter on the wire after digging it out of the loom
and checking voltage change between on and off - but I might be barking up
the wrong tree entirely here.

Heres's what the relay panel looks like:

13 - tall relay,    14 - tall relay     15 no socket    16 thermal breaker
  17 relay     18 no socket
 seat heater?          seat heater?                         windows?

1 no socket        2 no socket         3 warning chime      4 relay
 5 relay         6 relay

7 ->  10  no socket or retainer for one until you get to positions:
11  relay       12 short relay

Everything is present and accounted for except #3, the warning chime, which
doesn't affect the A/C except to raise the driver's temperature. Everything
else electrical also works! (Don't tell the Audi Gods!) Engine runs
oh-so-sweet from idle to red line.

The A/C works, blows cold out the correct vents, etc., but the compressor
(new) really loads the engine at idle. Once on the road, there isn't much
difference in gas mileage as reported by the trip computer, so the problem
SEEMS to be isolated to lack of correct setting of the idle with the A/C on.

OK, Audi gurus, the glove is on the table!

Best Regards,

Mike Arman