I had a similar situation. When was turned on the air conditioner, a strange smell appeared, especially in winter. At a high temperature, the smell became even more terrible. I felt a sharp smell of mold. I think the problem is in the fan shaft. There may be food there. I have small children. Maybe they could put something in there. I didn't find an answer to my problem. Therefore, I contacted the service center that installed an air conditioner for me in Singapore
socool.sg. They immediately said what the reason was. Solved the problem was only after using Lysol.