Lost inverter communications, the local fault. It is logged after 2 minutes with no communication between the outdoor control (AOC) and the inverter (MOC). It elevates to fault 48 after 3 consecutive failures within 20 minutes, or after 20 minutes of continuous loss of connection. The manual says to refer to fault code 48.
Carrier 33 on the Infinity 25VNA8 / 24VNA9 is lost inverter communication, the local fault. Count 3 short flashes and 3 long flashes. It is logged after 2 minutes with no talk between the outdoor control and the inverter, and it becomes fault 48 after 3 failures in 20 minutes or after 20 minutes continuous. The manual says to use the fault 48 checks: the harness between AOC plug PL20 and the MOC, electrical noise, and possible inverter damage. Furnace code 33 on a Carrier furnace is a limit switch. This outdoor 33 is not that.
Same characters, different appliance: Carrier 33 on a furnace is a different fault. Carrier furnace 33.
Likely causes
- The fault 48 list this row points to: a loose or disconnected harness between AOC plug PL20 and the MOC
- Radio or electrical noise
- Possible damage to the inverter
Safe checks for 33
- Count 3 short and 3 long before you pull the disconnect. Code 48 is 4 short and 8 long
- For radio or electrical noise, the fault 48 action says the system will try to self-mitigate with repeated start attempts
- Technicianverify the harness between AOC PL20 and the MOC. If the harness is good, the manual's action for possible inverter damage is to change the inverter drive
Capacitors can hold a charge after the power is off. Safety terms.
When to call a pro
Call a licensed HVAC technician. Code 33 is the earlier communications fault. Code 48 is the elevated lockout of the same problem.
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