2001 Buick Century AC compressor engages in defrost but not on vent or max AC

Hello, interesting, because at least the "max AC" mode should engage the compressor. I'm wondering what different route the electrical components take between defrost function compared to max AC function. Sounds like a possible climate control concern. Can you confirm the condenser fan turns on when turning on the defrost or max AC? Use this link to find some shops near you that can help with your concern: www.repairpal.com/repair-shops