700066 Roof Curb is simply the mounting frame that a commercial HVAC unit rests on when being installed on a rooftop. Constructed of high quality galvanized steel and many use the innovative tongue and groove MicroLok design, which requires no tools and assembles much faster than the competition's product. Includes the wood nailer for roofing, gasketing to provide a seal to the HVAC unit and duct supports and insulated deck pans, as required. The 700067 Low Ambient Kit extends operation of the compressor in the cooling mode when the outdoor temperature is less than 65?F which can cause the indoor coil to freeze up. The low ambient control cycles the outdoor fan motor in response to refrigerant pressure and conditions. It is designed to regulate condenser head pressure at low ambient temperatures by varying the amount of airflow through the condenser. 700068 Condenser Fan Motor is located in the outside unit. It's function is to move the air across the condenser coil to cool the refrigerant and change it from a hot gas into a liquid. 700091 Humidity Sensor (or hygrometer) senses, measures and reports the relative humidity in the air. It therefore measures both moisture and air temperature. Relative humidity is the ratio of actual moisture in the air to the highest amount of moisture that can be held at that air temperature. All products are drop ship only.