Carrier HVAC Error Code 42: How to Fix It
Medium 30-60 minutes Medium Severity
Verified June 2026
- Error Code
- 42
- Brand
- Carrier
- Product Type
- hvac
- Severity
- Medium
- DIY Difficulty
- Medium
- Estimated Fix Time
- 30-60 minutes
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Tools You'll Need
- Screwdriver (Phillips/flathead)
- Multimeter
- Voltage tester
How to Fix Error Code 42
-
Turn Off Power to the HVAC System
Always turn off power before working on electrical components to avoid shock or damage. -
Inspect Thermostat Wiring
-
Check Thermostat Compatibility and Settings
-
Examine the Blower Motor and Control Board
Only perform electrical tests if you are comfortable and have proper tools. If unsure, call a professional. -
Replace the Thermostat or Blower Motor Control Board
Replacing the control board or motor should be done by a qualified HVAC technician if you lack experience.
Parts You May Need
Thermostat (compatible with Carrier PWM communication)
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Blower motor control board
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Thermostat (compatible with Carrier PWM communication)
Check Price on Amazon
Blower motor control board
Check Price on Amazon
Thermostat (compatible with Carrier PWM communication)
Check Price on Amazon
Blower motor control board
Check Price on Amazon
Thermostat (compatible with Carrier PWM communication)
Check Price on Amazon
Blower motor control board
Check Price on Amazon
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When to Call a Professional
If the error persists after checking wiring and replacing the thermostat, or if you are not comfortable working with live electrical components, call a professional HVAC technician. A faulty control board or blower motor requires specialized tools and knowledge.Frequently Asked Questions
What does PWM signal lost mean on a Carrier HVAC system?
It means the communication between the thermostat and the blower motor via Pulse Width Modulation has been interrupted. This typically happens due to loose wiring, a faulty thermostat, or a defective blower motor control board.
Can I fix Carrier error code 42 myself?
Yes, many causes are simple to fix, like loose wires or a dead thermostat. However, if the issue is with the control board or motor, professional help may be needed.
How much does it cost to fix Carrier error code 42?
Cost varies: a thermostat replacement can be $50-$200, while a control board replacement may run $200-$500 including labor. Professional diagnosis is often $100-$200.
Is error code 42 serious on a Carrier HVAC?
It's moderately serious. The system will not operate properly until the issue is fixed. Ignoring it could lead to further damage or lack of heating/cooling.