A system is charged from a cylinder that turned out to hold two refrigerants mixed together. What is the likely result in that system?
- AThe two refrigerants separate in the receiver and the system settles back at its normal design pressures
Refrigerants do not sort themselves out by gravity in a receiver. The mixture circulates as its own substance with its own pressure and temperature relationship, matching neither original refrigerant.
- BThe compressor draws noticeably less current, because the mixture boils at a lower temperature than either refrigerant alone
Current draw is more likely to climb as the compressor works against pressures it was never built for. Expecting lower amperage reads contamination as a harmless efficiency change.
- COil returns faster to the compressor, which shortens run time but leaves no lasting harm to the equipment
Better oil return would be an improvement, not a symptom. Contamination changes the pressure and temperature behavior of the charge; it does not tune the system for the better.
- The system operates at pressures and temperatures it was never designed for, risking lost capacity and compressor damage
Why D is correct
Equipment is engineered around one refrigerant's pressure and temperature curve. A mixture shifts that curve, so charging targets, superheat, and subcooling no longer apply and the compressor may run well outside its intended conditions.
What this question is testing
Tests whether the candidate connects refrigerant purity to real machine behavior rather than treating contamination as a paperwork problem only.
On the job
Contaminated charges show up as callbacks that resist normal diagnosis: pressures that do not match any chart, superheat that cannot be dialed in, and a system that never quite cools. An identifier on the low side settles the question quickly. The repair is to recover the whole charge into a dedicated cylinder marked as mixed, replace the driers, evacuate, and recharge from a verified source, then bill the contamination separately.
Memory technique
One system, one refrigerant, one set of pressure charts. Break the first and the third stops working.
Exam tip
Pick the answer that describes the system running outside its design conditions. Choices claiming a mixture is harmless or beneficial are always wrong.
Where to look it up
Reuse limits in 40 CFR 82.156 exist because contaminated or mixed refrigerant is not fit for service in an appliance.