What is the job of the expansion valve or orifice tube?
- Pumping refrigerant and raising its pressure
- Metering refrigerant and dropping its pressure
- Storing refrigerant and removing moisture
- Cooling refrigerant with outside airflow
Show the answer
B. Metering refrigerant and dropping its pressure
The metering device is the dividing point between the high and low sides. It restricts the flow of liquid so the pressure falls and the refrigerant can boil at a low temperature in the evaporator.
Reference: Refrigeration cycle; metering devices
How does R-1234yf differ from R-134a?
- It is mildly flammable and has a much lower global warming potential
- It is non-flammable and has a much higher global warming potential
- It contains chlorine and has a much higher ozone depletion potential
- It runs at many times the pressure and needs steel lines throughout
Show the answer
A. It is mildly flammable and has a much lower global warming potential
R-1234yf was adopted because its global warming potential is a tiny fraction of that of R-134a. It is classed as mildly flammable, so it needs equipment designed for it. Neither refrigerant contains chlorine, and their operating pressures are similar.
Reference: Mobile A/C refrigerants; R-1234yf properties (A2L classification)
Technician A says R-134a and R-1234yf systems have different service port fittings to prevent cross-contamination. Technician B says an R-1234yf system can be topped off with R-134a as long as the system is relabelled. Who is correct?
- Technician A only
- Technician B only
- Both technicians
- Neither technician
Show the answer
A. Technician A only
Technician A is right: the unique fittings keep the wrong equipment and refrigerant from being connected. Technician B is wrong; refrigerants are never mixed, and a vehicle must be serviced with the refrigerant it was certified with.
Reference: Mobile A/C refrigerant handling; EPA Section 609