MACS 609 Certification Practice Exam

Under what condition can HFC-134a become combustible in a mobile air conditioning system?

1. When exposed to light

2. If shop air is used and HFC-134a is present

3. When it's excessively cooled

4. If mixed with certain oils

The correct answer is: If shop air is used and HFC-134a is present

HFC-134a, also known as tetrafluoroethane, is generally not considered combustible under normal conditions. However, mixing it with certain oils can lead to the creation of a combustible mixture. This is primarily due to the breakdown of HFC-134a at high temperatures, which can result from the presence of the oils used in mobile air conditioning systems. When HFC-134a is combined with certain lubricants or oils, the mixture can undergo chemical reactions that may produce flammable byproducts. The other conditions mentioned do not typically contribute to the combustibility of HFC-134a. For instance, exposure to light generally does not affect its flammability. The use of shop air alongside HFC-134a does not inherently cause it to become combustible either. Additionally, excessive cooling does not lead to combustion; rather, it might cause the refrigerant to condense into a liquid state without affecting its flammability. Thus, the condition where HFC-134a can potentially become combustible is indeed when it is mixed with certain oils.