Refrigerant system block or restriction

 Hello 
The first think you need to check is the high and low side pressures. Normal operating pressures on this unit running at temperatures of -5 to +5 degrees in the freezer and +37 to +44 degrees in the refrigerator. You should have 2-4 lbs. suction pressure and 125-135 high side pressure with a clean condenser. Remember on these units the condenser can be impacted and you cannot see it. We have run into this many time when you think the condenser is clean and it still affects the unit operation. We use a high pressure C02 tank with a wet towel across the back to catch the dust and dirt. Once you verify you have A CLEAN condenser, check your pressures. If you have low suction and discharge pressures you have A refrigerant leak or low charge.  If you are running into A vacuum on the low side -10 or lower and have A high side pressure of 160 lbs. or higher you have a refrigerant restriction. Most likely A capillary tube that has an oil restriction. You can then do two things. 1) Replace the heat exchanger with the capillary tube and filter dryer. 

2) Cut out the filter dryer and put the end of the capillary tube in a large jar. Cut the suction line near the compressor and braze on a process stub. Hook up your refrigerant tank and turn it upside down and blow liquid refrigerant through the suction line, evaporator and capillary tube. You will see oil going into the jar and this will flush all the oil causing the restriction. Let it flow until you have A steady white solid refrigerant stream. I personally have done this method over 100 times over the last 30- years and have been successful 99% of the time. There was one situation that the capillary tube was kinked. Matt Ace technician