MRCOOL mini split error code F6

Common causes

• The zone F indoor coil outlet temperature (T2B) 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 zone F indoor coil outlet temperature sensor (T2B) on the refrigerant line for zone F inside the outdoor unit, near the port it serves. 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 MRCOOL units show F6

This page applies to MRCOOL DIY 2nd/3rd Gen, DIY 4th Gen, DIY Multi-Zone, Advantage, Olympus and Easy Pro units on the multi-zone outdoor unit display. MRCOOL's own documentation lists F6 as "Zone F indoor coil outlet sensor (T2B) fault, shown on the outdoor display", the same definition used across the Midea multi-zone outdoor unit display 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 MRCOOL shows this code

The indoor display shows the code in place of the temperature. On DIY 4th Gen units a four-character code alternates between its two halves (EL, then 0C); write down both. The MRCOOL app also reports the current fault.

On the outdoor display, E codes are outdoor faults, F codes identify which zone's coil sensor failed (F1 = zone A, F2 = zone B, and so on), and P codes are protections.

Other MRCOOL codes

Same part of the system as F6:

All MRCOOL error codes

F6 on other brands

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

• Pioneer F6 Zone F indoor coil outlet sensor (T2B) fault, shown on the outdoor display
• Blueridge F6 Overload frequency limiting (protection)
• Zone Air F6 Compressor phase loss or reversed phase protection
• Daikin F6 High pressure in cooling (refrigerant overcharge)