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59 Cards in this Set
- Front
- Back
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When using R22 as a tracer gas, what is the recommended usage amount? What amount of nitrogen should be used? |
10 psi Then add nitro to 150 psi (never exceed system design pressure) Recommended to purge mixture afterwards |
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What is an advantage to pressure testing with a tracer gas? What is a disadvantage? |
Advantage is testing meters are good at picking up refrigerant leaks. Disadvantage is that the mixture cannot be calculated for temperature swings. So not ideal for long hold tests |
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What are some disadvantages of vacuum leak testing? |
Does not indicate leak location Pressure difference is small. Requires precise device Flux can plug leak |
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What should be taken into consideration when pressure testing and factoring in temperature change? |
Oil and leftover refrigerant in system will scew the temperature pressure readings. Especially with taking into consideration on service |
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Why use R22 as a trace gas? |
It has a heavier chlorine molecule. 410A has no chlorine Could also use R134 |
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What is recommended when using an ultrasonic leak detector? |
Need a wet coil to produce the whistle effect |
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What is a disadvantage to using UV dye for leak testing? |
UV dye can displace oil |
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Decay tests that rise from 500 to (up to) 50,000 microns and stops is an indication of what? |
Moisture in system |
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A decay test that rises from 500 to 760,000 microns indicates what? |
Leak |
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What are two convenient methods to speed up leak testing without taking apart ductwork/condenser covers? |
Cover outdoor unit with blanket place electronic leak detector under the blanket. Place electronic leak detector in evaporator drain outlet. Wait for 10 minutes on these tests. Refrigerant is heavier than air |
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Some leaks occur under standard conditions. These are known as ____________ leaks. Some other types of leaks are: |
Standing Temperature, pressure, vibration, combination (dependent), cumulative. |
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When using micro leak detector, what is indicative of a positive test? |
Foam Cocoon |
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What are some techniques to aid with leak detection? |
- blankets to trap refrigerant gases - increasing pressure (tracer and nitro, start compressor without condenser fan, warm water, block air intake during operation, place unit into defrost) - tap system components with mallet after applying micro leak detector |
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How are cumulative leaks detected? |
Helium mass spectrometer |
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True or false? Some leaks are considered acceptable within the industry |
True Micro leaks are considered an acceptable amount of leakage |
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True or false? Halide torches are no longer recommended for leak detection because it is dangerous |
True some refrigerant combinations are flammable and using open flame can release acidic compounds, but halide torches are becoming more ineffective as they are used for detection of chlorine which is not present in HFC refrigerants |
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Why does the EPA allow for trace gas to be purged after use? |
Because it is mixed with mostly nitrogen which is non condensible so infeasible for reclamation. Also, the refrigerant is being used to detect leaks… not being used as a refrigerant |
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The compressor is considered to be a part of the _________ side of the system and can be isolated when it has ___________________. |
Low side Service valves |
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How long after pressurizing a system for a pressure test does it take for the pressure to equalize before beginning the test? |
10 minutes before tapping the gauge and beginning the pressure test |
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What are the general standards for pressure test hold times? |
1 hour for small systems 24 hours for large systems I.e 10 ton split system |
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Aside from listening for the whistle of a leak, what is a basic method for detecting a leak without any equipment? |
Wet your hand and feel around the suspected leak locations. Leaking vapour will cause a cooling effect as the water evaporates off your hand |
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What technique may be superior to electronic leak detection when there is a significant amount of refrigerant in the surrounding area? |
Ultrasonic |
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What technique may prove useful in a situation where there is oil spots/soaking from previous leaks? |
UV fluorescent dye |
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Electronic leak detectors can detect leaks as small as about _______ oz per year. |
1/4 oz per year |
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What are some examples of system components that are subject to mechanical stresses that may cause leaks? |
- gas line on heat pump (hot in winter, cold in summer = expansion and contraction) - threaded connections, especially where expansion and contraction is more likely - high side close to compressor = vibration and heat plus cold ambient winter temps |
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What should be done before electronic leak testing the indoor components / low side of a system? |
Turn on the circulation fan without the compressor This will raise the system pressure depending on the ambient house temperature |
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What is the lower threshold for leaking systems requiring a repair? |
50 lb systems or larger MUST be repaired before recharging if they have a substantial leak (more than 35% loss per year) If the leak is less substantial than this the owner may leave it and must document it. If the upper threshold is reached, the owner has 30 days to rectify the issue. Comfort cooling chillers have different requirements |
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What is the allowable leak rate for comfort cooling chillers? |
15% loss per year Rectification requirements are to bring losses down below this threshold |
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The process of evacuation includes the removal of _____________ & _____________. What terms are given to these evacuation processes? |
Removal of oxygen and other non condensibles = degassing Removal of moisture = dehydration |
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What is the result of nitrogen in an hvac system? |
It is Non condensible so it will raise head pressures, increasing compression ratios and compressor operating temperatures, along with inefficiency |
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What is the result of nitrogen in an hvac system? |
It is Non condensible so it will raise head pressures, increasing compression ratios and compressor operating temperatures, along with inefficiency |
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What is the main concern with oxygen in a system? |
Production of acids resulting in deterioration of moving components, breakdown of motor insulation (causing shorts), and electroplating of the running gear (seize up bearings) |
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What is required before electroplating occurs? |
- acid - electrical current - dissimilar metals In refrigerant systems, this seems to only occur from copper to steel |
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Where in a system is sludge most likely to form? |
Hottest location: discharge valve |
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What happens when water is present in a system? |
Hydrolysis = hydrochloric OR hydrofluoric acid and more water are produced. This is non condensible and raises head pressure which in turn leads to formation of sludge as the acid+moisture+oil all mix. |
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Noncondensibles are removed from a system via _______________, whereas solids and sludge are removed from a system via _____________ |
Deep vacuum Filtration (filter driers) |
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How many microns are in an inch? |
25,400 microns |
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What is the saturation point of water at 14.696 psia? |
212 deg f |
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What is the saturation point of water at 5,171 microns OR 29.921 in. HG vacuum? |
35 deg f |
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What is 14.696 atmospheric pressure converted into microns? |
760,000 microns |
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What are some reasons a decay test gauge reading might rise after isolation of the system? |
- moisture present boiling off - refrigerant may be dissolved in the crankcase heater oil - leak |
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What happens to vacuum pump oil as it absorbs moisture? |
It’s ability to maintain a low micron seal diminishes as its vapour pressure rises |
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A vacuum pump can only pull ______ cfm through a 1/4 inch hose. |
0.8 cfm (doesn’t matter what size the pump is) |
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What style compressor is typically utilized in vacuum pumps? |
Rotary |
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What is the difference between 1 stage and 2 stage vac pumps? |
1 stage is pulling the vacuum through 1 level of oil. Second stage pulls the exhaust from the first stage through the second stage leading to less back pressure / lower intake pressure leading to deeper vacuums. |
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1 lb of water allowed to boil will produce ___________ cubic ft a vapour (at 70 deg f ) |
867 cubic ft |
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When performing a a triple sweep evacuation, how much nitrogen skills be added to break the vacuum? |
Add nitrogen to approx 20 in. HG then fire up the pump again. |
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Why is vacuum testing for leaks insufficient and bad practice? |
- if there is a leak it introduces air into the system - it does not indicate the location of a leak - can pull contaminants/flux buildup into a pinhole leading to an inaccurate test (false test) - this only proves that a leak is not present under a pressure differential of 14.696 psi |
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How do you know what size vacuum pump to use on a system? |
Square root of system capacity: I.e 25 ton system requires a minimum 5 cu ft pump. 16 ton system = 4 cu ft pump and so on |
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Why might ice form under a vacuum? |
Because the vapour produced during the boiling process can lead to increase in vapour density and reduction in temperature. This can happen if there is a significant amount of water present in liquid form |
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Aside from removing as much water as possible from a system before evacuation, What should be taken into consideration when there is moisture present? How might this affect the vacuum quality? |
Heat the system piping and components to be vacuumed as much as safely possible. If there are cold spots whatever moisture is trapped in the system will simply boil off from the warm spots and condense again in the cold spots. |
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Why is it a good idea to start up a compressor in the evacuation process? How would you do this? |
Because moisture can become trapped inside the compressor and get locked there due to the closed flapper valves. During a triple sweep evacuation I would isolate the system under vacuum. break the vacuum with nitrogen to at least atmospheric pressure. Then start the compressor for a few seconds to release moisture and gasses from the compressor Chambers. |
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What can result from running a compressor under vacuum? |
There is no insulation between the fusite terminals under a vacuum (oil and refrigerant are dielectric and typically act as an insulator in this location). Running the compressor like this can lead to short circuit and damaged motor windings |
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What is another cause for trapped water in a system/compressor during a deep vacuum? |
Water is heavier than oil and can become trapped under a layer of oil… preventing it from boiling off and dehydrating. This is why vibration can be a good tactic to loosen up trapped moisture Heat applied to the crankcase heater may also free up the moisture |
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What are two examples of restrictions that might lead to improper vacuums that appear to be deep vacuums? |
- closed valves (I.e. solenoid valves) which may isolate parts of the system - was going to say flex hoses but it seems these are more likely to leak under a vacuum leading to wrongly indicate a system leak. |
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What causes acid formation? |
Heat+refrigerant+moisture |
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What causes sludge? |
Moisture+acid+oil |
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True or false? CFC makes for a great tracer gas when pressure testing. |
False This is not permitted |
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What steps are involved in cleaning a system after a motor burnout? |
- reclaim/recycle refrigerant - change compressor - add temporary suction and filter line driers and monitor pressure drop across them - acid test the new compressor’s oil |
