Abstract: A Drain Trap Alarm for Heating Ventilation Air Conditioning condensate drain system includes a upstream port coupled to the cooling coil drain tray followed with a U-type trap and a downstream port coupled to the external atmosphere. The invention is provided with a liquid level sensor and continuously monitors the liquid level of drain trap. The signal from the liquid level sensor in communication with the microprocessor will notify operating personnel that the condensate drain is malfunctioning and activate the automatic prime valve to restore the dry drain trap condition to normal operation. The microprocessor provides operational test enabling the HVAC operating personnel to quickly test Drain Trap Alarm.