Ducane mini split error code E4

Common causes

• The indoor room temperature (T1) thermistor has failed (they do drift and fail with age and heat cycling).
• Its plug has worked loose from the control board, or a pin has corroded.
• The sensor lead is chafed, pinched or chewed, giving an intermittent open or short.
• The control board's sensor input has failed (rare compared with the sensor itself).

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.

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 the code comes straight back after a reset, the fault is real and not a glitch.
3. With power off, locate the indoor room temperature sensor (T1) just behind the front panel, on the air inlet side, usually held in a small clip. Follow its lead back to the board and reseat the plug firmly.
4. Inspect the lead for damage along its whole length, especially where it passes through the chassis.
5. If you have a multimeter, unplug the sensor and measure its resistance. A reading near zero ohms (short) or infinite (open) confirms a bad sensor. Most mini split thermistors read roughly 5 to 20 kΩ at room temperature, so a value in that range with a steady drift as you warm it in your hand means the sensor is fine and the board is the suspect.
6. Replacement thermistors are inexpensive and plug in. Match the part number from the parts list for your model.

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

Sensor swaps are a doable DIY job on most units. Call a technician if the sensor tests good and the code persists, because that points at the control board.

Which Ducane units show E4

This page applies to Ducane 4DHV outdoor with DWH wall-mount indoor (2016 and later) units. Ducane's own documentation lists E4 as "Indoor room temperature sensor (T1) open or short circuit", 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 Ducane 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 Ducane codes

Same part of the system as E4:

All Ducane error codes

E4 on other brands

The same characters do not always mean the same thing. Check the brand on your unit.

• Pioneer E4 Indoor room temperature sensor (T1) open or short circuit / Outdoor temperature sensor fault: coil (T3), ambient (T4), discharge (T5) or a zone coil outlet (T2B)
• Blueridge E4 Compressor discharge temperature too high / Indoor room temperature sensor (T1) open or short circuit
• Gree E4 Compressor discharge temperature too high
• Zone Air E4 Abnormal system operation or lack of refrigerant
• Daikin E4 Low pressure protection
• Mitsubishi Electric E4 Indoor unit signal receiving error (from remote controller)
• Carrier E4 Indoor room temperature sensor (T1) open or short circuit
• Trane E4 Abnormal system operation or lack of refrigerant / Indoor unit signal receiving error (from remote controller)
• Heil E4 Indoor room temperature sensor (T1) open or short circuit / Compressor discharge temperature too high
• ACiQ E4 Indoor room temperature sensor (T1) open or short circuit / Abnormal system operation or lack of refrigerant