Lennox mini split error code PC 04
Inverter compressor drive error. Also shown as PC04.
- TypeProtection
- SystemCompressor / inverter
- Can I fix it?Technician job
- Applies toMCB / MWCB indoor unit display
What PC 04 means on a Lennox
The inverter lost control of the compressor: it would not start, lost sync, or drew current the drive could not regulate.
On this platform, PC 04 is a protection: the system stopped or throttled itself to prevent damage; many clear on their own once conditions return to normal.
Common causes
- A locked or failing compressor.
- Loose or corroded compressor terminals.
- A failed inverter board or IPM.
- Low voltage during compressor start.
- Liquid refrigerant flooding the compressor after sitting in the cold.
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.
- If you own a multimeter and are comfortable using it, measure the supply voltage at the outdoor unit's L1 and L2 terminals with the unit running. A 230 V system should read roughly 208 to 253 VAC.
- Listen on restart: a hum with no compressor start, or a buzz then silence, points at the compressor or drive.
- Do not repeatedly reset; each failed start stresses the drive.
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
Technician job. Ask for winding resistance and drive output checks before agreeing to a compressor replacement.
Which Lennox units show PC 04
This page applies to Lennox MPA / MPB / MLA single-zone, MPA / MPB / MLA multi-zone, MCB / MWCB, MWMA / MWMB, MCFA / MCFB and MMDA / MMDB units on the MCB / MWCB indoor unit display. Lennox's own documentation lists PC 04 as "Inverter compressor drive error", 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 Lennox shows this code
MCB / MWCB indoor unit display: 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 Lennox codes
Same part of the system as PC 04:
PC 04 on other brands
The same characters do not always mean the same thing. Check the brand on your unit.
- Pioneer PC 04 Inverter compressor drive error
Questions people ask
Can I reset a Lennox PC 04 code myself?
Yes. Turn the system off at the breaker for five minutes, then restart it. If PC 04 comes back, the fault is real and needs the checks above.
Is it safe to keep running a Lennox showing PC 04?
Not repeatedly. A protection code means the unit stopped itself to prevent damage, and resetting it over and over can turn a cheap repair into a compressor failure. Reset once, check the basics, and stop if it returns.
What will a technician check for PC 04?
Technician job. Ask for winding resistance and drive output checks before agreeing to a compressor replacement. Ask for the measurements, not just a parts quote.
Sources
- Lennox Corp1816-L7 Mini-Split Systems Service Manual: Indoor and Outdoor Unit Error Codes (MPA/MPB/MLA, MWMA, MCFA, MMDA), 10/2020
- Lennox MCB / MWCB Mini-Split Service Manual (error code table 2.1)
Updated September 2026. Codes and definitions vary by model year. If your manual disagrees with this page, your manual wins. Send a correction.