Two technicians are discussing refrigerant lines. technician a says that line connections must be tight but not so tight that air can't get through. technician b says that all connection o-rings have to be replaced when retrofitting a system to r-134a. who is correct?

The correct answer is: technician B, all connection O-rings have to ve replaced when retrofitting a system to R-134a.

Explanation:

When we have a refrigerant line, the refrigerant is used through a refrigeration cycle. Refrigerant should pass in a physical process of transformation, it should be pure, avoid another kind of phenomena.

When we are retrofitting a system to R-134a, it is thus necessary to change all connection O-rings. In that way, we can prevent the refrigerant of crossed contamination with other refrigerants or substances.

Let's analyze the opposite situation, if we do not change the O-rings and we change the refrigerant, probably there will be a few previous substances, which can react, or create other phenomena when they undergo the refrigeration cycle with the R-134 a. We have to avoid this situation. 

answer is: nuclear fusion produces elements that are heavier than helium.

nuclei combine to form a heavier nucleus, releasing energy.  

for example, fusion of hydrogen atoms at the sun.  

this fusion nuclear reaction is in the inner core of the sun and hydrogen (atomic number 1) is conveted into helium (atomic number 2).  

the inner core is the central region of the sun and all solar energy is produced in the core by nuclear fusion.