How do I troubleshoot a sub-zero freezer that is frosting up excessively?

To troubleshoot a Sub-Zero freezer that is frosting up excessively, follow these steps:
1. Check the door gasket: Ensure the gasket is intact and seal the door properly to prevent warm air from entering.
2. Inspect the defrost heater: Test the defrost heater for proper operation. A malfunctioning heater can lead to excessive frost buildup.
3. Clean the condenser coils: Dust and debris on the coils can hinder proper cooling and defrosting. Clean the coils using a coil brush or vacuum cleaner.
4. Verify the defrost timer: Test the defrost timer to ensure it is advancing correctly and initiating defrost cycles.
5. Monitor the temperature: Ensure the freezer temperature is set correctly to prevent frost accumulation.
If the issue persists, consult a professional Sub-Zero technician for a thorough diagnosis and repair.