The oil in a vacuum pump should be changed _____. a. about ...

[SGallaher96]

The oil in a vacuum pump should be changed _____.
 
  a. about every five minutes of pump operation
  b. only when changing from one refrigerant to another
  c. immediately after pumping down a wet or contaminated system
  d. about every 25 hours of pump operation

Question 2

It is important to clean dross and carbon deposits from a cut surface before welding because they can _____.
 
  a. produce extremely hazardous fumes during welding
  b. form hard, brittle zones and porosity in the weld zone
  c. damage certain welding equipment components
  d. cause molten metal to be blown considerable distances

[Zebsrer]

Answer to Question 1

c

Answer to Question 2

b

[SGallaher96]

Thank you!

[Zebsrer]

Always glad to help...