Fan coil or PTAC heat pump heats in Cool mode or cools in Heat mode

Last updated: August 18, 2026

Why this can happen

If a fan coil, PTAC, or similar heat pump system heats when Mysa is set to Cool, or cools when Mysa is set to Heat, the system may need a configuration that controls the heat pump reversing valve correctly.

This can happen even when the thermostat wiring appears correct, especially on heat pump systems with more than one fan speed or terminals that combine heating and reversing-valve functions.

What to check first

  1. Turn the system off if it is running the wrong mode.

  2. Confirm that the wiring has been installed according to the Mysa setup flow and any instructions provided by Mysa Support.

  3. Confirm the exact equipment type. A fan coil, PTAC, or heat pump may need different configuration than a conventional furnace or air handler.

  4. Have the system make, model, and wiring schematic available before contacting support.

What Mysa Support may ask for

Mysa Support may ask for photos of the previous thermostat wiring, the Mysa wiring, and the HVAC control-board schematic. This helps confirm whether the system needs a heat pump configuration with reversing-valve control and whether a two-fan-speed setup is supported for that equipment.

Important

Do not keep trying random configuration codes if the equipment is heating in Cool mode or cooling in Heat mode. The safest next step is to contact Mysa Support with the system details so the correct equipment type and configuration can be verified.