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
>