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Just wanted to know if anyone has found a refrigerant leak with a electronic leak detector with the system charged and running but not have a pressure drop with just nitrogen in the system?
I am curious because I had a small walk in R404A total charge 3 pounds 8 ounces and it is a pump down. It is for a laboratory so they are putting different items in the walk-in but I only saw instruments in there. Service call comes in for not maintaining temperature which is set at 35 degrees it was 58 degrees in the walk in. Unit was low on charge I added approximately 12 ounces of refrigerant. I did a electronic leak search and every time the system would come out of pump down the leak detector would go off it I put the probe close to the indoor coil. I took the detector outside and then came back in and cycled the system again a few more times and the detector would go off every time. When the system pumped down which was about 6-7 psig the detector was not picking up anything. The suction pressure was 62 psig when the system was running near set point. I checked the braze joints and the detector did not pick up anything in either pump down or running mode.
I let the customer know what I found and said I recommend replacing the evaporator coil, customer opted to replace the indoor section not just the coil. A employee who works there said he wanted to do his own test on the evaporator coil when we remove it and he put it in the shop on a bench and pressurized it (I don’t know if he used nitrogen) to 300 psig and called in about 2 weeks later and said that the coil is still holding at 300 psig and I misdiagnosed the leak and ripped them off. I had to go over the leak search with my boss because they are holding payment but I never got to talk to the employee at the lab. I have read about system dependent leaks and I have used dye to find leaks that I could not find with a nitrogen pressure check or a electronic leak detector or a combination of the two but I also never had a customer do their own test like this. I just would like to get some feedback from other techs that have found leaks with a electronic leak detector and not a standing pressure check. Thank you.