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