Your main responsibility is to always perform a job to the best of your ability. Installers take out and replace equipment. Service techs fix equipment and explain how to keep equipment running at it's best. Be respectful to the customer and always leave a job cleaner then when you got there.
The primary functions will vary depending on your job title. Installers primarily do install work . Service Techs will do system start ups and servicing on ventilation systems , air conditioning , control systems and heating equipment . Many service technicians concentrate on one or two of the skills ie ; primarily air conditioning or heating .. HVAC techs work for service companies , schools , hospitals and various other industries often as part of a maintenance team