I'm not sure I completely understand the issue. When you select defrost, regardless of the setting on the climate control, it will turn on full heat and direct it to the windshield. Even if the A/C is on when the defroster is selected, you will get heat.

Now if you are can't turn the heat off without defrost selected, then there is an issue.

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Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record