I have a residential split A/C unit with R22 refrigerant that it not cooling and shows ice forming on the high pressure line.
(I have read the rules concerning DIY but I'm trying to learn the workings of an A/C system and I live on an island with no 'pros' so I hope someone will still give me some suggestions or an explanation were to look for.)
Small description of my findings: When the A/C is switched on the pressure on the low pressure line almost goes into vacuum and the high pressure line shows ice forming. The ice forming starts directly after a small (capillary?) tube in a dual loop that sits in between the condenser and the connection point for the tubing to the indoor unit.
What I have understood so far from Internet sources is that the flow from the condenser to the evaporator is metered by a thermostatic expansion valve (TXV) or a capillary tube to reduce the 100% sub-cooled liquid high pressure refrigerant to a low pressure liquid vapor mixture that subsequently enters the evaporator where it boils off and extracts heat.
I have never read that the TXV or capillary tube is located in the outdoor unit, it is always located just before the evaporator in the indoor unit. But I have checked the indoor unit and found no metering device so the double looped capillary coil I found in the outdoor unit must be the metering device. Has anybody ran into a system like this and agrees with me?
From the fact that the high pressure line starts forming ice just at the boundary between the capillary tube and the normal tubing that goes to the indoor unit I conclude that the refrigerant already starts boiling off at this boundary and therefore cooling the high pressure line. I can think of two reasons why this is happening: 1) the capillary tube is clogged restricting the liquid flow, or 2) there is not enough refrigerant in the system.
I hope you can give me a suggestion what the problem might be or what to check or measure to rule out possibilities. As I said, there are no 'pro's' here and I'm very interested to learn A/C system.