24VNA6 / 25VNA4 seriesCarrier 66 fault code (24VNA6 / 25VNA4)

VFD Control Relay Coil Open; VFD Control Relay Coil Shorted

1. Code 66-41 VFD Control Relay Open Lockout

   The PCM commands the VFD to close a relay in the power circuit during VFD initialization. If PCM senses the VFD relay coil is open this code is set. While this code is active the VFD will not be powered and system is inoperable. 12VDC is fed from Pins 6&7 of the PCM into pins 5&6 at the VFD via communication cable as long as system is ready to run (other faults that stop system from operation are not active).

   24VNA6-25VNA4-1SM, p. 20

2. Code 66-42 VFD Control Relay Shorted Lockout

   The PCM commands the VFD to close a relay in the power circuit during VFD initialization. If PCM senses the VFD relay coil is shorted to ground this code is set. While this code is active the VFD will not be powered and system is inoperable. 12VDC is fed from Pins 6&7 of the PCM connector into pins 5&6 of the VFD connector via communication cable as long as system is ready to run (other faults that stop system from operation are not active). Check to ensure comm harness is not damaged and shorting to ground or another wire. To troubleshoot this fault, remove the PCM-VFD harness from the PCM while leaving the other end connected to the VFD. Check the resistance between the pins 6 & 7 of the harness connector. The resistance should be approximately 720 ohms. If the resistance is much lower than 720 ohms, then remove the connector at the other end of the cable from the VFD. Check the resistance between pins 5 and 6 of the comm cable connection at VFD. If this resistance is significantly lower than 720 ohms, then the problem is within the VFD. VFD Related Faults General Info Occasional VFD faults may occur that are caused by specific external circumstances. In these cases the VFD will self-recover and continue to operate normally. Once faults escalate to malfunctions permanent damage may be present. The service person should use judgement when replacing components to determine if occasional external conditions are present or if equipment is damaged and require replacement because system is not providing expected performance.

   24VNA6-25VNA4-1SM, p. 21