accent

When I turn on the air conditioner on my automatic 2001 Accent, the
transmission will shift really rough on low speeds. It sounds like I
am stuck on a low gear when accelerating and I hear a thunk sound when
slowing down. The check engine light is on solid but it will go off if
I drive without AC.

What is going on?

hyundaitech

The first step in diagnosis is probably to retrieve the engine and
transmission codes.