When I answered in the beginning, I thought it was under the hood. Now I know it is inside.
Condenser coils and throttle body are outside under the hood.
You need to clean the evaporator, heater core, and all the ducts. You can remove the cabin filter and try spraying some cleaners in that area.
I just attached the TSB for the filter. You do not have one. GM dropped that option in 2003.
Roy
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Friday, February 21st, 2020 AT 5:06 AM