First lets explain the refrigerant system performance test. Refrigerant (people also call it Freon...which is a brand name not an actual product) can't be measured with a dipstick. It must be weighed to know how much is present. Every refrigerant system has a specific weight of refrigerant that is needed for it function properly. If this level is too low or too high the system will not function properly. Basically it wont work well. So we recover the refrigerant from a system and see how much the removed refrigerant weighs. For this we use a very specific machine called a Coolant or Refrigerant Recovery and Recycle Machine. They run about $4k-$8k which is why most shops charge around $100-$150 for this service. Once we have the recovered weight we can then check and see if it matches what is required by the car manufacturer for that model. If it was low we can assume their was a leak or a recent repair to the system. If it's high we can assume someone added refrigerant to the system. Both results mean we need more information from the customer. We ask questions about smell, sound, performance, time frame since it failed, recenter repairs, etc.
Next we perform leak tests under vacuum. If the system fails to maintain a specific amount of vacuum over a measured period of time then we know somewhere in the system a leak is present. Next we charge the system and look / listen for any signs of leaks. We also add refrigerant oil and dye to the system. If the system has a very small leak this dye will help us identify it as time passes.
Finally we check the electrical circuits. Sometimes ac compressors work intermittently due to failing sensor, damaged wiring or improper computations by the control unit. We use our scan tool to monitor inputs and outputs at the control unit making sure they match what we should see occur as we operate all of the HVAC controls. This includes testing door positions and sensor readings for the dash ducting. We also check the compressor clutch or control valve for proper operation. During all of this we are looking for signs of a leak.
So what does a leak look like? Most of the time it will look like a wet part that has a saturation of oil. The oil is often clear or green (dye) and usually shows up anywhere to hoses connect or where a line changes from a metal tube to a rubber hose. Another place leaks occur is between the case halves of ac compressors. In some cases leaks occur where welds are weak and crack such as on condensers and evaporator cores.
In this video we show how we found a failed evaporator core using a $40 camera from a large online shopping site. The camera is called an endoscope and can be super useful for finding leaks in tight places or in locations that would require a lot of labor to access. In about 20 minutes we proved that the evaporator core was the source of the leak for this client. We knew to look there because we had a good conversation with our client about what they were experiencing who allowed us to complete a refrigerant system performance test. By asking questions about smell, sound and operation we knew there was a possibility of an evaporator core leak. The performance test confirmed a leak was present in the system somewhere and our endoscope allowed us to see it all before any major work was performed. Now our client knows exactly what the failed part is and what it will cost for us to replace it for him. No guessing, no parts swapping, just pure evidence.