Hi everyone.
I'll try to be short:
Before some time ,i bought a used mini-split system,with "electrical problem",at least that said the man from which i bought it.But when i went to get it ,he said also that not long ago,the conditioner was out of refrigerant,and some guy "repaired" it quite cheap.After i bought it and went home,while i was preparing for recovering the refrigerant,i saw that there was a leak from the two valves of the outdoor unit,so i have recovered the refrigerant (there was about 300gr (R407C) of 870gr as pointed by the nameplate) and changed the valves.I was purging nitrogen while i was brazing the new valves,so that no oxidation scales can form and possibly plug the cap tubes.After that i performed few times a nitrogen blow from both valves and evacuated to 150 microns (it took about 7-8 hours).Then i charged it to the name plate's charge with scale and ran it - everything was fine-it was heating the room fine,the current consumption was OK-perfect.Then i left it for few days,and when i had some free time,i decided to test it again,and the problem arised - when i turned it on in heating mode,there is no heat.In heating mode,the thicker pipe should be hot (it's the discharge line - hot gas),but it wasn't.I've checked the pressure-only 15 barg (normally it should go to 20-25barg,according to the indoor/outdoor conditions).Also when i stripped the covers ,i found that the common cap tube's end(there are two cap tubes and one check valve-in heating mode,the refrigerant passes trough both of them,and in cooling,it passes only trough the one of them (common) and the other is bypassed by the check valve) was frosted together with 10-15cm of the pipe after it.Since the charge was right,the only two options for this scenario are plugged cap tube or moisture which freezes inside the cap tube.Since checking for freezing moisture was easier ,i grabbed the hot-air gun and heated the cap tube and the frosted pipe,and voila-everything went fine again...until the next long period of not using the conditioner,and the outside temperature drops about 0deg C.Few days after,i unbrazed the cap tubes,the outdoor heat exchanger and the tubings and blown them with nitrogen,than evacuated to 150 microns again (3-4 hours),charged and nothing changed.Then i tried to evacuate again,but this time i was heating the compressor's bottom with hot-air gun to make the evaporation of moisture of the oil easier (at 150 microns ,the water needs to be about 50deg C to boil),but still no luck.
Finally i added a filter drier and sight glass with moisture indicator at the liquid line ,but again that doesn't solve the problem - the sight glass is green i.e no moisture,but the problem is still present.
My guess is that once the system was out of refrigerant,it was left open for too long for some reason,and moisture was left in and since it's a R407C system and uses POE oil ,which is hygroscopic,now the moisture is in the oil,and it cant get out.
My last hope was the filter drier,but since it doesn't solve the problem,i'm out of suggestions,and i need advice.
Any help would be appreciated.
Thanks in advance.