I went to a call on swimming pool heat pump system, which was icing up.

When I got there, it was switched off and after only a couple of minutes of running it iced up from the TEV to the evaporator. Client said that was exactly what it was doing before. I wanted to prove it was gas charge/leak, so I added a very small amount of refrigerant to see what happened. Literally a gauge line of R22, cleared the iced all the way to the distributor, another line cleared the distributor. At this point i´m thinking, that it must have a small leak somewhere. I left it running for an hour, and everything seemed to working. Went to get the leak detector from the van, and when I got back it had stopped. It restarted again, a minute or so after then tripped 5 or so minutes later, while I was trying to find out what was causing it to trip it must have started an stopped 5 or 6 times. There is only a suction service port nothing else so only one place to take a pressure reading. Safety devices are HP, LP, Water flow, and low ambient temp.

I went back yesterday, armed with a line tap valve, which I was going to put on the discharge stub for the HP switch. Get a reading, then braze up once I knew what the problem was. It didn´t trip once yesterday, I ran it for 2 hours non-stop while I was there, and it´s still running now. So I don´t know what was causing it. I think It may have been HP, but I can´t prove that.

Here´s some readings I got yesterday,
Ambient air temp: 19ºc
Suction Pressure: 57psi
Discharge Pressure: 275psi
Suction Temp (at TEV bulb): 1.3ºc
Discharge temp (Compressor): 77.3ºc
Liquid line temp (off condensor): 23.8ºc
Water inlet temp: 21.6ºc
Water outlet: 22.4ºc

The unit is 8 years old, no idea on make, model or anything as there are no data plates. I got the gas type (R22) from the compressor label. System has never been worked on before. I´s assured there is good water flow as everything on the water side has tested (apparently). Have I missed anything obvious?

P.s. the line-tap valve will be cut off, it´s just there for test purposes.