What is access panel?

The access panel is a device that is designed to provide check the valve, air hose and other air condition systems. It works to increase the efficiency of air conditioning units by check the air condition systems working.

A ceiling is the most common location for an access panel. 
One is also sometimes installed on walls or ceiling. The type, size, and location of the access panel depends on many factors. These include the layout of the building or room, location of walls and ceiling, and type of air conditioning system being used.
The desired look and function of the air conditioning diffuser will also affect how and where it is placed.

What is volume control damper(VCD)?

Volume Control Damper or VCD is a specific type of damper used to control the flow of air in an HVAC heating or cooling system. 

In order to improve efficiency and occupant comfort, HVAC systems are commonly divided up into multiple zones. For example, in a house, the main floor may be served by one heating zone while the upstairs bedrooms are served by another. 

In this way, the heat can be directed principally to the main floor during the day and principally to the bedrooms at night, allowing the unoccupied areas to cool down.

Ducting systems must often provide a method of adjusting the volume of air flow to various parts of the system. Volume control damper, not to be confused with smoke/fire dampers, provide this function. 

Besides the regulation provided at the registers or diffusers that spread air into individual rooms, dampers can be fitted within the ducts themselves. These dampers may be manual or automatic.

Volume Control Damper provide automatic control in simple systems while variable air volume (VAV) allows control in sophisticated systems.