b4 Blower motor trip (lost rotor control or high current)

What the control is telling you

The blower motor lost rotor control or saw high current and shut down. Furnace will not run. ComfortNet thermostat shows MOTOR TRIPS b4.

Applies to: GMVC95/AMVC95 upflow and *CVC9 counterflow two-stage furnaces

Likely causes

• Sudden load change on the motor
• Sudden blockage of the furnace air inlet or outlet
• Very high load: blocked filter, very restrictive ducts

Test and repair steps

1. Safety turn power off before working on the control or wiring.
2. Check the filter, return grilles, registers, ducts and the furnace inlet and outlet for blockage.
3. Clear the restriction and run the furnace again.

Settings for these units

• Normal status displays (7-segment) · Goodman/Amana GM9S96/AM9S96
• Normal status displays (7-segment) · Goodman/Amana GM9S80/AM9S80
• Normal status displays (7-segment) · Goodman/Amana GM9C96/AM9C96
• Minimum recommended filter size · Goodman/Amana GM9C96/AM9C96

Models that show this code

10 models in Goodman/Amana *MVC95/*CVC9 two-stage ComfortNet

Other codes on the same units

• b0 Blower motor not running
• b1 Lost communication with blower motor
• b2 Blower motor size does not match model data
• b3 Blower motor limiting (power, temperature or speed)
• b5 Blower motor locked rotor
• b6 Blower motor over/under voltage or over temperature
• b7 Blower motor missing parameters
• b9 Low indoor airflow