2006 Honda Civic air condition

My AC isn’t cold. Honda says it’ll take $600 to fix–the plate between the heating and AC elements is not functional.

“the plate between the heating and AC elements is not functional.”

Huh?
Can you ask the mechanic again for the diagnosis?
This terminology makes no sense to me.

I second what VDCdriver said.

I’m unfamiliar with a “plate” between the heating and AC elements.

Could you be talking about the “blend door,” which controls airflow within the HVAC system and thereby regulates interior temperature?

Before you pay dealer prices for repairs, you may want to consult with an independent automotive HVAC shop. It might save you some money, regardless of the actual cause of your problem.