Ameristar mini split error code P4
Excessive outdoor discharge temperature.
- TypeProtection
- SystemCompressor / inverter
- Can I fix it?Homeowner checks, then maybe a tech
What P4 means on a Ameristar
The refrigerant leaving the compressor got too hot. The compressor stops to protect itself.
On this platform, P4 is a protection: the system stopped or throttled itself to prevent damage; many clear on their own once conditions return to normal.
Common causes
- Low refrigerant charge.
- A blocked outdoor coil or failed fan.
- A partly closed service valve.
- A failing compressor.
How to fix it yourself
Work through the checks below first; they resolve most cases. If they do not, the repair itself may need a technician.
- Look at the outdoor unit: clear leaves, cottonwood fluff, snow or ice from the coil and make sure the fan can spin freely and nothing is stacked against the cabinet.
- Confirm the service valves are fully open.
- Cool down with power off for 30 minutes and retry.
- Anything inside the refrigerant circuit (sensors are fine, but valves, compressors and leaks are not) needs EPA-certified refrigerant handling. That is a technician job.
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
Recurring P4 with a clean coil needs a charge check.
Which Ameristar units show P4
This page applies to Ameristar M4TXK / M4MXW hi-wall inverter units. Ameristar's own documentation lists P4 as "Excessive outdoor discharge temperature", the same definition used across the TCL platform 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 Ameristar shows this code
The indoor display shows the code in place of the set temperature. E codes are faults: something has failed and needs diagnosis. P, H, d and F codes are protections: the system stopped or throttled itself to prevent damage, and many clear on their own once conditions return to normal.
Other Ameristar codes
Same part of the system as P4:
P4 on other brands
The same characters do not always mean the same thing. Check the brand on your unit.
- Pioneer P4 Inverter compressor drive error / Compressor discharge temperature protection (outdoor display)
- Blueridge P4 Inverter compressor drive error
- Zone Air P4 Excessive outdoor discharge temperature
- Daikin P4 Inverter heat sink temperature sensor fault
- Mitsubishi Electric P4 Drain sensor or float switch fault
- Trane P4 Excessive outdoor discharge temperature / Drain sensor or float switch fault
- ACiQ P4 Inverter compressor drive error / Excessive outdoor discharge temperature
Questions people ask
Can I reset a Ameristar P4 code myself?
Yes. Turn the system off at the breaker for five minutes, then restart it. If P4 comes back, the fault is real and needs the checks above.
Is it safe to keep running a Ameristar showing P4?
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.
Do I need a technician for Ameristar P4?
Work through the checks below first; they resolve most cases. If they do not, the repair itself may need a technician. Recurring P4 with a clean coil needs a charge check.
Sources
- Trane Mini Split HW Inverter Service Manual (4TXK / 4MXW), SVM027A-EN, 2024, 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.