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MODEL OVERVIEW
About this model: Midea MAT12H2ZWT
MAT12H2ZWT 230-V wall air conditioner with electric heat: seven PDF codes and operating checks.
Check capacity and electrical identity
MAT12H2ZWT is the 230-volt, through-wall Midea air conditioner with both cooling and electric heat. Midea lists 12,000 BTU for cooling and 11,700 for heating, and markets this size for a room of up to 550 square feet. The 24.21-inch depth, 20.28-inch width, 14.35-inch height and 78.28-pound product weight matter when identifying an existing wall sleeve or planning safe removal. These numbers distinguish it from the smaller MAT10H2ZWT that appears on the same family manual cover. The exact listing now says the model is no longer available, but the manufacturer still links its manual through the product page. Compare the installed plate with MAT12H2ZWT before using a code table; a similar control face can belong to a cooling-only sibling. Any electrical supply or wall opening decision belongs to a qualified installer.
Understand heating without confusing modes
The family controls show Auto, Cool, Dry, Heat and Fan. A note says cooling-only family members lack Heat; this exact product page explicitly describes Cooling with Electric Heat, so that exclusion does not apply to MAT12H2ZWT. In Heat mode, the requested temperature is set with the up/down controls, while fan speed may be restricted on some variants. The general setpoint range is 62–86°F. In Fan Only, the display reports actual room temperature instead of the chosen setpoint, and HI or LO can be a room-reading limit rather than a diagnostic error. Dry mode keeps fan control automatic at low speed. If the machine seems to change operation unexpectedly, first record its selected mode and whether the reading is ambient or set temperature before assuming the electric heater or room sensor has failed.
Use scheduled controls to explain apparent stops
This model's listing promises automatic restart with recent settings after power is restored. A restart following an outage can therefore reproduce an old mode or temperature without anyone touching the panel. The timer can schedule start and stop, with half-hour steps to ten hours and hour steps up to twenty-four; switching the unit on or off or resetting the timer cancels the schedule. Sleep mode changes the target by 2°F after thirty minutes and another 2°F after a further thirty, then maintains it for seven hours. Energy Saver lets the fan continue three minutes after compressor shutdown and later runs it for two minutes at ten-minute intervals. Those fan cycles should not be mistaken for the E3 fan-stall code. Keep track of active icons, timer and recent power events before calling a service center.
Interpret the display and remote thermostat
The Check Filter lamp illuminates after 250 operating hours. Clean the filter and press its button to clear the reminder; the lamp is not one of the seven sensor and control faults. C-SENSE works from the remote only and uses the temperature at the remote's location, transmitting it every three minutes. If that signal is not received within seven minutes, the unit beeps and exits the function. A remote left in sun or moved to another room can therefore change apparent comfort without any internal sensor fault. The manual also lists separate remote versions, one marked without HEAT for cooling-only appliances. Match the remote to the heater-equipped unit before using its menu as evidence about the appliance. If an actual AS or oS appears, record the exact case and letters rather than substituting a remote symptom.
Match each of the seven fault strings
On PDF page 32, AS describes the room-temperature sensor, ES the evaporator sensor and HS the electric-heating sensor. CS points to an outdoor-unit condenser sensor in the shared control text; oS is also labelled a room-temperature sensor error, so retain the distinct display letters in a service report. E3 is fan stall, and E0 is an EEPROM parameter failure. The printed advice for every one is to unplug and reconnect, then call service if the message repeats. That limited owner action does not authorize opening a wall-mounted electrical appliance or replacing a sensor. If heating alone is weak, note whether Heat mode was selected, the power supply was normal and HS actually appeared. If cooling alone falters, note the same conditions with ES or CS. Avoid converting HI, LO or the filter reminder into fault codes.
Verified model details
Exact 12,000/11,700 BTU heat-cool model
Source for this detailSeven codes checked on PDF page 32
Source for this detailHI/LO and Check Filter are different from faults
Source for this detailEnergy Saver and C-SENSE can explain changes in operation
Source for this detail
This description summarizes the linked source documents; check each cited source for your exact model and region.
Manufacturer source
Open official source
Midea 12,000 BTU 230V In-Wall Air Conditioner with Heat MAT12H2ZWT
Open official sourceIf there is a safety risk, stop using the appliance and follow the manufacturer’s instructions.