30,000BTU air-handler & condenser (1988 Carrier) A/C only. I know that when the sys. comes on, there's alot of bubbling & hissing of the refrig. lines as the freon pressureizes. However, it should dissapear at a point. I've got air-bubbles in the lines after the comp has been running for an hour straight.
The bubbles will go outside & can be seen thru the observation glass, then will come inside & can be heard right where the high-pressure line connects to the evap. coil. Then the whole thing repeats; the inside gets quiet, but the bubbles go back outside.
Had the system evacuated in May 2004, but the SAME problem exists. The split is better & the air is colder, but I've still got bubbles. I saw the tech guy drain the freon back into the canninster & use a vaccume pump too.