What does 4 flashes mean?
High temperature limit switch has tripped due to overheating.
Common causes
- Dirty air filter
- Blocked vents
- Blower motor failure
- Blower capacitor failure
- Improper duct sizing
Diagnostic & testing steps
- 1. Replace dirty air filter immediately
- 2. Check all registers are open and unobstructed
- 3. Verify blower motor runs properly
- 4. Test blower capacitor
- 5. Allow to cool 30 min, check limit switch continuity after cool down
Tools required
- Multimeter
- Capacitor tester
OEM parts & part numbers
High Limit Switch, Blower Capacitor, Blower Motor
Part numbers: B1370108, B1340018
Safety warning
⚠️ CARBON MONOXIDE RISK: Repeated limit trips indicate heat exchanger stress. Inspect for cracks.
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