You can have a fuse that is acting up. Even when they look good, these fuses can be intermittant. Replace them all with new. (The default mode for the climate control is heat.)

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Benzmac:
Donnie Drummonds
1991 GMC Syclone
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM