To view the ductwork in 3D, go back to drawing M1 and go to
View 
Viewports 2 Viewports
You will be asked for a configuration option. Select "Vertical". Place the cursor in the right viewport to activate it. Go to
View 3D Views SW Isometric
Zoom in until your drawing matches the one shown below.
To view the right drawing in 3D, go to
DM HVAC Sections and 3D Drafting Draw 3D Ductwork
Design Master HVAC will prompt you to draw a crossing box around all the ducts to draw in 3D. In the left view port, draw your crossing box over all the ducts in the drawing.
To view the hidden lines, select the right viewport and type HIDE at the command line. Your drawing should match the one shown below.
You may use the DM HVAC Layer Management commands to turn the duct centerlines, double lines, and 3D layers on and off. Remember that when the hidden lines are drawn you cannot zoom or pan in the drawing. You must first type REGEN at the command line. Setting hidden lines for plotting purposes is done using a different set of commands, which is discussed further in the Plotting Hidden Lines page on our website.
Congratulations! You now know how to perform the basic 3D functions using Design Master HVAC.
See My Project has a Database for important notes about working with your project drawing and database files.