Refrigerant Leak Detection Quiz

Ten questions on finding refrigerant leaks and proving the repair. Pick an answer to see whether you are right and why. Related reading: The Code: refrigerant rules.

1. A leak is suspected and the system still holds refrigerant. A sensible first step is to:

   1. Add refrigerant and leave
   2. Check likely leak points with an electronic leak detector, then confirm with bubble solution
   3. Replace the compressor
   4. Vent the system

   Check the usual suspects with a detector and confirm with bubbles. Topping off without finding the leak only delays the next service call.

2. A standing pressure test is normally done with:

   1. Oxygen
   2. Dry nitrogen
   3. Compressed shop air
   4. Propane

   Dry nitrogen is inert and free of moisture. Oxygen can react violently with oil, and shop air brings moisture in with it.

3. During a nitrogen pressure test, the pressure should:

   1. Never exceed the test pressure the manufacturer specifies for the equipment
   2. Be as high as the regulator allows
   3. Be 1 psig
   4. Be applied without a regulator

   Always use a regulator and stay within the manufacturer's test pressure. Too much pressure can damage components or cause injury.

4. Bubble solution is most useful for:

   1. Pinpointing the exact location of a leak
   2. Measuring the charge
   3. Finding leaks inside a coil you cannot reach
   4. Measuring vacuum

   Once you know roughly where the leak is, bubbles show the exact spot. Give it time, because small leaks form foam slowly.

5. Common leak points on residential systems include:

   1. Schrader valve cores, flare nuts, service valves, evaporator coils and lines rubbed through by vibration
   2. Thermostat wires
   3. Air filters
   4. The blower wheel

   Mechanical connections, valves and spots where copper vibrates against metal are frequent leak points. Evaporator coils can also develop corrosion leaks.

6. Formicary corrosion is:

   1. Corrosion in copper tubing, often in evaporator coils, that causes tiny pinhole leaks
   2. Rust on the outdoor cabinet
   3. A thermostat fault
   4. Oil breakdown

   Formicary corrosion eats tiny tunnels through copper and has been linked to certain organic acids in indoor air. The leaks are very small and hard to find.

7. An ultrasonic leak detector works by:

   1. Detecting the high-frequency sound of gas escaping from a pressurized leak
   2. Sensing refrigerant chemicals
   3. Measuring temperature
   4. Using ultraviolet light

   It listens for the hiss of escaping gas, so it works with any pressurized gas, nitrogen included. Background noise makes it harder to use.

8. UV dye leak detection:

   1. Shows leaks as glowing spots under a UV light, but only use a dye the equipment manufacturer allows
   2. Works without any light source
   3. Is required on every system
   4. Seals leaks permanently

   The dye travels with the oil and shows at the leak under UV light. Some manufacturers restrict additives, so check before you add anything.

9. An electronic leak detector alarms near a joint. The best practice is to:

   1. Confirm the exact spot with bubble solution before repairing
   2. Add refrigerant right away
   3. Trust it completely
   4. Turn it off

   Electronic detectors can false-alarm on other vapors and drafts. Bubbles confirm the exact location before you cut or braze.

10. After repairing a leak on a system that was opened, the right sequence is:

    1. Pressure test, evacuate to the required vacuum, then recharge by weight
    2. Recharge immediately without evacuating
    3. Top off until the pressure looks right
    4. Run the system without gauges and see

    Prove the repair is leak-free, dry the system with a deep vacuum, then weigh in the correct charge and verify it.