§393.79 requires every CMV to be equipped with a windshield-defrosting and defogging device adequate to remove frost, ice, snow, and fog from the windshield. The rule is functional, not prescriptive — a vehicle passes §393.79 if the defrost actually keeps the windshield clear under operating conditions.
Severity weight
Severity weight 1 in the Vehicle Maintenance BASIC. The finding rarely stands alone — when an inspector reaches §393.79, they have usually also touched §393.78 (wipers) and §393.60 (glazing).
How it gets cited
The pattern is a defrost system that has been "good enough" for the season — a fan running but the heater core leaking, a duct kinked behind the dashboard, a blower at speed 1 only. In winter inspections, a windshield that fogs faster than the defrost clears it is the citation.
How to prevent it
- Test defrost performance during pre-trip in cold weather. If the windshield does not clear in a reasonable time at the highest setting, the system is out of spec.
- Replace cabin air filters on the maintenance schedule; a clogged filter starves the defrost.
- Check the heater hoses and core for slow leaks every annual inspection — coolant smell in the cab is a §393.79 risk months before it becomes a §393.83 exhaust risk.
How Roadworthy HQ helps
A defroster citation shows up in Roadworthy HQ as part of the inspection it came from, not as a record of its own: the app does not store individual violation codes. Log the roadside inspection on the vehicle's Inspections tab: date, state, level, driver, the number of violations, and whether it was out-of-service. For an out-of-service inspection the 15-day §396.9(d)(3) repair-certification countdown stays on that tab until you enter the certification date. The rule's 15 days cover every violation on the report, not only out-of-service ones, so for a non-OOS inspection that date is yours to track. The repair itself goes in the vehicle's maintenance log: date, type, what was done, who did it, and cost. DVIRs are logged per vehicle with the defect described in your own words, and a defect marked safety-affecting that is logged without a repair certification sends a critical alert.