Armstrong Air mini split error code P4

Common causes

• A locked or failing compressor.
• Loose or corroded compressor terminals (a loose spade under the terminal cover is common on older units).
• A failed inverter drive board or IPM.
• Low supply voltage during compressor start.
• Liquid refrigerant flooding the compressor after it has sat in cold weather.

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.

1. 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.
2. 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.
3. Listen at the outdoor unit on restart. A hum with no compressor start, or a short buzz then silence, points to the compressor or its drive.
4. Do not repeatedly reset and retry. 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

Compressor and inverter drive diagnosis is a technician job. Ask for compressor winding resistance and drive output checks before agreeing to a compressor replacement.

Which Armstrong Air units show P4

This page applies to Armstrong Air 4DHV outdoor with DWH wall-mount indoor (2016 and later) units. Armstrong Air's own documentation lists P4 as "Inverter compressor drive error", the same definition used across the Midea platform (classic 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 Armstrong Air shows this code

The code appears on the indoor unit's LED display in place of the set temperature. Some models also blink the indicator lamps in a pattern that matches the code. E codes are faults in the indoor unit or its communication link, F codes are faults on the outdoor side, and P codes are protections: the outdoor unit has stopped itself to prevent damage. EC is the refrigerant leak check.

Other Armstrong Air codes

Same part of the system as P4:

All Armstrong Air error codes

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