Q: We’ve noticed out refrigerant line is freezing up at night. We just recently had it charged, which helped so that it no longer freezes up in the day time, but still does at night. The technician recorded the R410A service valve pressures at 340 psig and 99 psig during the day (90 degF ambient). He said the suction pressure was low, but sub cooling was good at 10 degF. He believes the low suction pressure is responsible for the freezing at night. The compressor trips off at night after icing up the suction line, presumably due to low pressure. After a couple minutes it turns back on and trips again in another few minutes, and continues to cycle this way. The tech is recommending that we upgrade our coil from a 4 to a 5 ton. Currently, all components are 4 ton. He says this will increase the pressure. Will this work, and is this the proper remedy? Please explain.

It sounds like the expansion valve is bad. The superheat has to be off and the oil temperature high, which is bad for the compressor. The coil doesn’t need to be replaced especially with a 5 ton. The 4 ton matched system is better for humidity control. Replace the expansion valve and this should fix the problem.