Code 128 — Low Pressure Switch Open

What does 128 mean?

This fault indicates that the low-pressure safety switch has opened, signaling that the refrigerant pressure in the system is too low. This can lead to system shutdown to protect the compressor.

• Refrigerant leak (undercharge)
• Frozen indoor evaporator coil
• Restricted refrigerant flow
• Faulty low pressure switch
• Insufficient airflow over the indoor coil

Click steps to track your progress.

1. 1

   Check and replace dirty air filters to ensure good airflow over the indoor coil.

2. 2

   Visually inspect the indoor coil for ice buildup; if frozen, turn the system off and allow it to thaw.

3. 3

   Turn off the HVAC system at the thermostat and then at the circuit breaker for 30 seconds, then restore power.

4. 4

   If the issue persists, contact a qualified HVAC technician immediately, as this often indicates a refrigerant leak or system blockage.