I have an ducted split unit (1.5TR) installed in the bed room. The unit was not cooling adequately. Our AC maintenance technician went near the condensing unit, connected his refrigerant manifold to the service port of the suction line, and the other end of the line to open air and sprayed away (refrigerant/oil??) and kept monitoring the manifold gauges. After spaying out for some time, the cooling became back to normal.

I asked him what is being evacuated from the system, for which his response was excess oil! My doubt here is, since suction line is under negative pressure when the system is running, how is it spraying out? Shouldn't it be sucking in as in the case of refrigerant charging? Also, what is the probability of oil reducing the cooling efficiency of the unit.

service port (suction).jpg