Air Conditioning - Foam in sight glass

Can anybody think of a plausible reason why a system would be pumping foam (as viewed through sight glass on high pressure line) when it's not undercharged?

The system (Trane XE-900) hasn't cooled particularly well for years, and never reaches set temp on hot (90+) days. Discharge air temp is rarely more than ~10 degrees below room temp even on the mildest days. I had a filter/dryer and sight glass installed in April, and a triple evac done on the notion that the system might have had moisture from the beginning. In March, both the A-coil and the condenser were THOROUGHLY cleaned.

The tech can't explain the foam in the line. All he says is it must be something with the A-coil (??). There is no THX valve. He swears the system is not undercharged. Is it possible for the A-coil orifice to have become larger than it's supposed to be? The unit is 17 years old.

Pressure & temp readings today:
Low side 76
High side 160
Outside air temp 81
Inside air temp 73 (no wet bulb therm avail)
discharge air temp 62
Static press (unit off 5 minutes) 102 (both sides)

Thanks for any ideas.

Did the Tech check the superheat & subcooling levels? As this will give you a more accurate reading of what is going on inside both coils. Head pressure of 160 is a bit low.

17 years old put freon in to clear up the sight glass. That old ill bet has a receiver in it for freon. High side a160 I can see why it dont cool to good. Can high side in the compressor be going out on you???????

ED ;)

I agree with Ed. I think the system is undercharged. Was the charge weighed in per the label on the unit? The compressor valves could be going out as well but that is just a guess without further testing.

I think you need a new tech!
You cannot use a sight glass on a system with a fixed orifice or cap tube.