Cars will forgive you when you run your oil past the recommended changeout. Compressors will not. The difference is that in addition to carrying away heat and lubrication, the oil has the added function of having to handle all of that entrained air under extreme pressure. Oxidation of the oil is inevitable, and if the oil is not changed regularly, the oil will varnish the inside of the compressor, which will inhibit the unit from cooling properly. Change your oil at a regular interval, and only use compressor oil which is made to handle this extreme temperature, pressure and air entrainment.