American Standard mini split error code EP
Outdoor compressor casing top (overload) fault.
- TypeFault
- SystemCompressor / inverter
- Can I fix it?Homeowner checks, then maybe a tech
- Applies to4TXK / 4MXW / 4TYK series
What EP means on a American Standard
The thermal protector on top of the compressor opened. The compressor is being protected from overheating.
On this platform, EP is a fault: something has failed or is disconnected and needs diagnosis.
Common causes
- A blocked outdoor coil or failed fan.
- Low refrigerant charge.
- A partly closed service valve or restricted line set.
- 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.
- Let it cool with power off for 30 to 60 minutes.
- Confirm both service valves are fully open.
- 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
If it returns with a clean coil and a running fan, a technician should check the charge.
Which American Standard units show EP
This page applies to American Standard 4TXK / 4MXW / 4TYK hi-wall inverter and Mitsubishi Electric-built units units on the 4TXK / 4MXW / 4TYK series. American Standard's own documentation lists EP as "Outdoor compressor casing top (overload) fault", 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 American Standard shows this code
4TXK / 4MXW / 4TYK series: 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 American Standard codes
Same part of the system as EP:
EP on other brands
The same characters do not always mean the same thing. Check the brand on your unit.
- Zone Air EP Outdoor compressor casing top (overload) fault
Questions people ask
Can I reset a American Standard EP code myself?
Yes. Turn the system off at the breaker for five minutes, then restart it. If EP comes back, the fault is real and needs the checks above.
Is it safe to keep running a American Standard showing EP?
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.
Do I need a technician for American Standard EP?
Work through the checks below first; they resolve most cases. If they do not, the repair itself may need a technician. If it returns with a clean coil and a running fan, a technician should check the charge.
Sources
- Trane / American Standard Mini Split HW Inverter Service Manual (4TXK / 4MXW), SVM027A-EN, 2024
- Mitsubishi Electric M-Series service manuals (self-diagnosis tables)
Updated September 2026. Codes and definitions vary by model year. If your manual disagrees with this page, your manual wins. Send a correction.