[HayZee518]

oil just doesn't evaporate, look for spots or a coating on any piping in the area of the compressor. leaking oil will compromise your compressor and anything inside that moves and is lubricated. freon will leak out along with the oil. valves can be reed type or valves like in a car if the system is big enough. reed valves use a tempered spring steel sheet with a spring plate behind it. have your tech put gauges on the system and measure high side and low side pressures. a high gauge that oscillates indicates a leak.