Walk-in cooler was temping at 44 degrees upon arrival. took down Slimline cover and found inside evaporator coils were extremely Dusty. Remove power to the fans and brushed out heavy dust and blue the rest out with nitrogen. turn the unit back on, had bubbles in sight glass. charge was a little low. Added 8 oz of R22 refrigerant and checked for leaks. No leaks detected at this time. I adjusted the thermostat to turn off at 34 degrees and on at 39 degrees. Recommended to general manager that all three walk-in units should be heavily cleaned. Please provide quote for General Manager to provide preventive maintenance on the walk-in coolers and freezer.