A sudden drop in room temperature when switching a Mitsubishi heat pump from cooling mode to heating mode could be due to several factors:
Initial temperature reading: When you switch the heat pump from cooling to heating mode, the temperature sensor or thermostat may take some time to adjust and accurately reflect the new room temperature. During this adjustment period, there might be a temporary discrepancy between the actual temperature and the displayed temperature.
Heat pump startup: Heat pumps typically go through a startup process when switching modes. During this process, the heat pump may temporarily blow out cool air before the heating cycle begins. This initial blast of cool air can create a perception of lower room temperature, even though the heating operation is starting.
Temperature difference: Heating mode on a heat pump works by extracting heat from the outside air and transferring it inside. If the outdoor temperature is significantly colder than the desired indoor temperature, it may take some time for the heat pump to reach and maintain the set temperature. As a result, the room temperature can drop temporarily until the heat pump can generate sufficient warm air to raise the temperature to the desired level.
Fan speed: When the heat pump switches modes, the fan speed may change as well. If the fan speed decreases during the transition from cooling to heating mode, there may be less air circulation in the room, which can create a perception of lower temperature.
Sensor placement: The location of the temperature sensor in the heat pump system can also affect the accuracy of the displayed room temperature. If the sensor is placed in a less representative or poorly insulated area, it may not accurately reflect the overall room temperature, leading to discrepancies between the displayed temperature and the actual temperature.
If you continue to experience significant temperature discrepancies or concerns with your Mitsubishi heat pump, it's advisable to consult the product manual, contact the manufacturer's customer support, or seek assistance from a professional HVAC technician to ensure proper functioning and accurate temperature control.