Of course, Mark is most likely right on how to address this issue.  

Wanting to help, let me give you my experience from the dark side:  that's right, a Subie 2.2 motor.  Was having an issue with motor quitting when A/C was on, like coming to the end of a freeway offramp and suddenly putting clutch in.  Turns out, it was a mechanical issue.  On the Subie motor, there is something called an Idle Air Control Valve.  Over time, these things get gummed up with old oil vapors and high temperatures.  A thorough cleaning to remove gunk, and now motor quickly drops into the 1500 RPM range, and then also gently proceeds down to idle RPM.  Perfect.  No more quit.  I felt like an expert!
I think the WBX motor must have a similar type device.  Some Idle Device that maybe needs a thorough cleaning.  Just throwing this out there.

    On Saturday, July 10, 2021, 6:46:13 PM PDT, vw_van_fan_Mark <madvws@cox.net> wrote:  
 
 The compressor clutch needs a control wire from the A/C wiring to turn
the compressor on/off as needed.
The wire I was talking about is an additional wire feeding over to the
true fuel injection harness for idle speed control use.
The wire over to the fuel injection harness connects to a thin
white/green wire coming out of the injection harness under the ignition
coil.

Mark

Ryan Cresawn wrote:
> Thanks Mark. I see the single wire laying across the top of the compressor.
> The end coming from the fuel injection wiring harness is connected to the
> end coming from the compressor. The two meet and lay on top of the
> compressor. I suppose I could begin with a simple continuity test from one
> end to the other. Does that seem like a good next step?
>
> Ryan
>
> On Sat, Jul 10, 2021, 10:31 vw_van_fan_Mark <madvws@cox.net> wrote:
>
>> A first step would be to check the wiring at the new compressor.
>> VW runs a single wire from the fuel injection harness over to the
>> compressor clutch so the injection system can know when the A/C
>> compressor is loading down the engine.
>> That is how the idle control system knows when to speed up the idle for
>> A/C.
>> They may have simply overlooked that signal wire to the idle circuit.
>>
>> Mark
>>
>> Ryan Cresawn wrote:
>>> On July 6, 2020 I hired a shop to fix my factory AC in my '91 Vanagon
>>> camper with 2.1l engine. The old compressor was leaking and the shop
>>> replaced it. At 11.5 months into a 12 month warranty the AC wasn't
>> cooling
>>> well. I returned to the shop last week. They identified a refrigerant
>> leak
>>> in the compressor and replaced it under warranty. I picked up the Vanagon
>>> yesterday and was told that I need to hire a shop to fix the low idle
>> when
>>> the compressor is on.
>>>
>>> I drove the Vanagon home and confirmed that when the compressor was
>> running
>>> the idle speed of the engine would drop from around 900-950 to about
>>> 600-650. The engine did not stall but it felt like it was close to
>>> stalling. How should I begin to troubleshoot this issue?
>>>
>>> Thanks in advance,
>>> Ryan
>>>
>>
>