Carrier mini split error code PC 40
Communication error between outdoor main board and inverter board. Also shown as PC40.
- TypeFault
- SystemCommunication
- Can I fix it?Technician job
- Applies toindoor display, four-character codes (newer units)
What PC 40 means on a Carrier
The two boards inside the outdoor unit (main control and compressor driver) stopped talking to each other.
On this platform, PC 40 is a fault: something has failed or is disconnected and needs diagnosis.
Common causes
- A loose ribbon or plug between the boards.
- A failed driver board or main board.
- Water or corrosion on the board connectors.
How to fix it yourself
Do the reset and the visual checks, but the underlying repair needs a technician with a meter and the service manual.
- Reset the system: switch the breaker (or the outdoor disconnect) off, wait a full five minutes so the boards fully discharge, then switch it back on and restart from the remote.
- With power off, open the outdoor service panel and reseat the connectors between the boards.
- Look for water intrusion or corrosion.
Switch off power at the breaker before opening either unit. Capacitors in the outdoor unit hold a charge for several minutes after power is cut.
When to call a technician
Board-level fault; a technician should test and replace the failed board.
Which Carrier units show PC 40
This page applies to Carrier Comfort 38MHRB / 40MHHQ, Comfort 38MGR / 40MGQ, Performance 40MAQ / 38MAQ, Infinity 40MPHA / 38MPRA and Carrier multi-zone units on the indoor display, four-character codes (newer units). Carrier's own documentation lists PC 40 as "Communication error between outdoor main board and inverter board", the same definition used across the Midea platform (four-character codes) it is built on. If your unit shows a code with a different shape (for example a four-character code, or a plain number), it is from a different table; use the lookup with your exact code.
Where Carrier shows this code
indoor display, four-character codes (newer units): The display shows a two-letter prefix and a two-character suffix, either together (EH60) or alternating (EH, then 60). Write both parts down; the suffix is what identifies the fault. EH and EL are indoor-side faults, EC is an outdoor-side fault, and PC is an outdoor protection: the unit stopped itself to prevent damage.
Other Carrier codes
Same part of the system as PC 40:
PC 40 on other brands
The same characters do not always mean the same thing. Check the brand on your unit.
- Pioneer PC 40 Communication error between outdoor main board and inverter board
Questions people ask
Can I reset a Carrier PC 40 code myself?
Yes. Turn the system off at the breaker for five minutes, then restart it. If PC 40 comes back, the fault is real and needs the checks above.
Is it safe to keep running a Carrier showing PC 40?
The unit will usually refuse to run, or run with reduced output, until the fault is cleared. Repeated resets do not fix anything and can mask a problem that is getting worse.
What will a technician check for PC 40?
Board-level fault; a technician should test and replace the failed board. Ask for the measurements, not just a parts quote.
Sources
- Carrier 38MHRB Single Zone Ductless Service Manual SG-38MHRB-01 (Diagnosis and Solution section)
- Carrier 40MAQ / 38MAQ High-Wall Ductless Service Manual 40MAQ-01SM (Diagnosis and Solution section)
- Carrier 40MPHA / 38MPRA Infinity High Wall Ductless Service Manual (error code table)
Updated September 2026. Codes and definitions vary by model year. If your manual disagrees with this page, your manual wins. Send a correction.