Midea AC / Heat Pump Error P4 – Inverter Compressor Drive Error
P4 (PC 04 on newer displays): the outdoor board couldn't drive the inverter compressor and stopped it.
At a glance
Severity: High
- Meaning
- Inverter Compressor Drive Error
- Typical repair cost
- $0–$3,200
- DIY difficulty
- Hard
Midea's code tables describe P4 as an inverter compressor drive error – shown as PC 04 on units with the newer four-character display. The outdoor board spins the compressor by feeding it three precisely timed phases from its power module and watches the resulting current to track the rotor. When the current goes abnormal, the rotor loses step or the compressor won't start, the drive gives up and P4 appears. Three things account for most cases: the power module or outdoor board, the compressor itself, and the three compressor leads between them. Poor supply voltage and high-pressure overload from a blocked outdoor coil or a stopped outdoor fan can tip a marginal drive over the edge. On fresh installs, closed service valves can make the compressor stall on start.
How it looks on the display
Model families & display variants
| Model family | Shows | Note |
|---|---|---|
| Wall units with 2-character display | P4 | The older Midea notation for the inverter compressor drive error. |
| Newer units with 4-character display | PC 04 | Same fault in the newer P-C notation; the PC codes group compressor and outdoor protections. |
| Midea-built units sold under other names | P4 / PC 04 | Many OEM mini-splits share the table; confirm with that brand's manual. |
Safety first · Consult a professional
The outdoor board and compressor leads carry several hundred volts DC, and the capacitors hold it for minutes after power-off. Owners should stick to the breaker, the disconnect and cleaning the coil with the power off. Refrigerant checks require an EPA 608-certified technician.
- Unplug the appliance or switch off the breaker before opening any panel. Mains voltage can kill.
Symptoms
- P4 or PC 04 on the indoor display
- Outdoor fan runs but the compressor clicks, hums briefly or doesn't start at all
- Unit cools for a short time and then stops, repeating the cycle
- Code appears on the very first start after installation
- All heads of a multi-zone system stop together
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Power module (IPM) or outdoor control board fault
- Compressor winding or mechanical fault
- Compressor lead plug loose, burnt or phases swapped
- Low or unstable supply voltage
- Overload from a blocked outdoor coil or stopped outdoor fan
- Service valves closed or refrigerant problem causing the compressor to stall
Fix it step by step
Watch the start sequence
Start cooling and go to the outdoor unit. Note whether the fan starts, whether the compressor makes any sound and after how long P4 appears. A hum or click followed by silence within seconds points to a start failure; P4 after minutes of running points to overload or voltage.
Rule out the supply
Make sure the unit is on its own breaker and the disconnect is fully on. P4 that only shows up when other big appliances start suggests the voltage is dipping – mention it to the technician.
Clear and clean the outdoor unit
With the disconnect off, clear debris from the coil and check nothing blocks the fan. Rinse the fins from the inside out with a garden hose. A clean, free-breathing coil takes load off a struggling drive.
Tools: Soft brush, Gloves
One long power reset
Switch off the breaker for 10 minutes to let the board discharge fully, then start once. If P4 returns immediately, don't keep restarting – repeated failed starts can overheat a compressor that is already weak.
Technician checks leads, module and windings
The technician checks the compressor plug and lead order, tests the power module terminals for shorts, and measures the compressor windings – low, a few ohms at most, equal between all three pairs and fully isolated from ground. That decides board versus compressor.
Tools: Multimeter
How to reset P4
- Turn the unit off with the remote
- Switch off the breaker for 10 minutes
- Restore power and start once; if P4 appears again at once, leave it off and call a technician
Where the parts are
- 1Fan
- 2Temperature sensor
- 3CAN bus
- 4Outdoor unit
- 5Compressor
- 6Engine computer (ECM)
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Clean outdoor coil | Yes | $0–$150 |
| Technician diagnosis | No | $120–$250 |
| Repair compressor lead plug | No | $150–$350 |
| Outdoor control / inverter board replacement | No | $400–$1,000 |
| Compressor replacement incl. refrigerant work | No | $1,500–$3,200 |
Rough US estimates; technician call-out fees vary by region. Not a quote.
When to call a technician
Call an HVAC technician if P4 returns after a clean coil and one long reset, and especially if it appears on every start within seconds. On a unit still under warranty, keep the model and serial numbers ready – boards and compressors are usually covered when the install was registered and done to the manual.
Frequently asked questions
Is P4 always the compressor?
No. The drive board is at least as likely, and a loose compressor plug is a cheap fix that must be checked first. Only measurements of the windings and the power module separate the options.
What's the difference between P4 and PC 04?
Nothing in meaning – newer Midea displays use four characters and group compressor-side protections under PC. Both point to the inverter compressor drive.
Why did P4 appear right after my new install?
On a new install, closed service valves, a lead plug knocked loose in shipping or a supply circuit that is too weak can all stop the compressor from starting properly. The installer should check those before any part is replaced.
Sources
- Official Midea user documentation and support pages (facts only; wording is our own)
- Methodology: How We Build Code Pages · Data Sources We Use · Editorial Policy