HVAC Study

The typical TXV comes factory set for 8-12 degrees of evaporator superheat, which in most cases should be fine. What is the correct setting for evaporator superheat? While it is true lower superheat will make the evaporator more efficient, we need to be more concerned with the compressor or total superheat. If we check the superheat on the suction line 6” from the compressor we should normally have at least 20 degrees of total superheat. This will ensure the compressor is not slugging with liquid even when frost is present. The suction line temperature at the compressor should not exceed 65 degrees to ensure proper compressor cooling. The last but most important reading is the discharge line temperature taken 6” from the compressor. This temperature should never exceed 220 degrees, as higher discharge temperatures will lead to compressor failures. Reducing superheat will lower both the compressor suction line and discharge line temperatures.

On the low side gauge: R-22: 64 - 81 PSIG R-410a: 110 - 136 PSIG On the high side gauge: The range is a lot wider based on seers. The higher seer rating, the lower psig. The lower seer rating, the higher psig. R-22: 100 - 300 R- 410a: 230 - 325 Cannot charge the system by pressure only due to the cooling days. You will definitely have to look at the superheat. Use subcooling to charge system if TXV Use superheat to charge system if Piston The normal subcooling should be between 8 to 12 degrees. If the target subcooling is not available, then you can normally assume that the target subcooling is 10 or 11, and you should shoot for 11. The target superheat should be calculated using this formula: (indoor web bulb temperature x 3 - 80 - outdoor dry bulb temperature) / 2, this will normally give a fairly accurate target superheat, but if the target superheat is posted on the machine or the machine has a superheat target chart, then the chart should be used, the calculation wont be necessary