Walk in Freezer problems

Hello,

Before I begin I would like to state I am not proud of what happened in this situation but I would like to learn from it and get some input from you guys. I have been working refrigeration as a tech for a little over a year now.. I was sent to look at a walk in freezer this morning having issues cooling. The evap coil was clear and all fans running. Thermostat was checked and working. Went on roof and checked condensing unit and found bubbles in the sight glass. I hooked up my gouges and found my pressures to be low. Looking at the condensing unit I saw writing for the unit to be r502, r22, or r404a. After looking at previous job notes I found we have been going back and recharging the system with MO99 as it has a leak in the system somewhere. So I decided to add MO99 in the system. I was always taught to charge the system until the sight glass was full, so I kept adding more and more charge until my tank was empty and sight glass was still not full. I thought it was weird that I just added 20+ pounds of refrigerant to it. My low side pressure was at 20 and high side 225. I decided to look at older history on the unit and found the compressor was changed out in 2016 and charged with 404a. I checked the TXV and found it rated for r502. I called my boss and asked about it, and the freezer was cooling and down to 10 degrees at this point. I was told to just pack up and leave and if we get a callback we will flush the system out and recharge it. I know it is not the correct solution, but I packed up and left. I would like to know how the system was still working with a different refrigerant for so long and what you guys think the best course of action is. Again I know this is not right and I am not proud of it, but would like to use this as a learning experience and grow from this. Thanks

submitted by /u/jmomy
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