I am working in fire fighting field but now i am planning to shift to hvac field .I don''t have much idea about this system .Can any one share about material that will be helpful to beginners like me..
If you are serious about this, enroll in a Mechanical Engineering course. In the end, you will want a PE license and that requires a bachelor of science in Engineering degree in the United States at least.
If you are looking to pay for courses and get certificates, EPIC runs a good introductory course. ASHRAE also offers courses, both online/self study and some in class stuff.
These two websites offer online courses (the content is free to look at but you can pay and get certificates also):