Liquid line restrictions refer to restrictions in the portion of the refrigerant system carrying the subcooled liquid from the condenser to the evaporator. They most often occur at some point where the potential for restriction exists like filter/dryers and metering devices. The symptoms are “starving” evaporator which appears as low suction pressure and high superheat. Head pressure will be normalish to lower but subcooling will likely be high. It all depends on the degree of restriction.
If the restriction is at the metering device, the distributor lines may frost. A severely restricted LL filter will create frost. If a restriction causes the pressure to drop well below the boiling point pressure of the liquid temperature, some of the liquid will flash causing a significant drop in temperature.
This example was heat pump running in the heat cycle. I knew it was a restriction because the subcooling was high. I pumped the charge into the indoor coil and broke the Chatleff coupling and found the piston bore blocked by some piece of contaminate.
I’ve seen only one example of 3/8ths tubing restricted. I was on a really old condenser (decades). The problem was visually obvious. On opening up the tubing the restriction was an accumulation of black stuff…don’t ask me what.
Wayne
HeatPumpClinic.viewmonster.com
Good video
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