I'm working on a walk in freezer. I found unit low on ***** mp66. did not have mp66 so I used hot shot 2. pulled a vacuum down to 500 microns. started charging unit. about 30 mins later my compressor went off on external overload. I cooled compressor down with ice. found mars relay 64 burnt contacts. replaced relay and also installed a hard start cap. after compressor cooled down it started. again after about 1hr or so it went off on over load .I tried adjusting expansion valve to lower super heat. super heat was high. also there is a hold back valve on suction line. I I did not change liquid line filter. could there be a slight restriction in dryer causing super heat to be high. Im going back tomorrow to change filter dryer and start all over. can any one give me some advise