A refrigerant recovery system comprising: an oil separator including a chamber configured to receive refrigerant from an air conditioning system; a heat exchanger, which also functions as a compressor oil separator, disposed within the oil separator; a compressor including a low pressure side fluidly connected to the chamber and a high pressure side fluidly connected to the heat exchanger; a compressor suction conduit and a compressor suction hose being connected in series and connecting the chamber and the low pressure side of the compressor; a compressor discharge tube and a compressor discharge conduit being connected in series and connecting the high pressure side of the compressor and the heat exchanger; a compressor oil return conduit and a compressor oil return hose connected in series and connecting the heat exchanger to the compressor; a first flow line that is fluidly connected to an inlet of the oil separator and connectable to a source of refrigerant; a first valve disposed in the first flow line; a second valve disposed in the compressor oil return conduit; and a controller operably connected to the compressor, the first valve, and the second valve and configured to, in a preheating operation, operate the first valve to open to enable a predetermined amount of refrigerant to pass into the chamber of the oil separator; activate the compressor; operate the second valve to open so that a flow loop for the predetermined amount of refrigerant is formed between the heat exchanger and the compressor comprising in this order the compressor, the compressor discharge tube and conduit (124, 164), the heat exchanger and the compressor oil return conduit with the second valve and the compressor oil return hose; and subsequently commence a refrigerant recovery operation, wherein the controller is further configured to periodically initiate a compressor oil return process during the refrigerant recovery operation to return compressor oil collected in the heat exchanger to the compressor, wherein the controller operates the second valve to open and the compressor to generate a constant suction in the compressor oil return conduit, thus urging the compressor oil collected in the heat exchanger through the compressor oil return conduit and the compressor oil return hose back into the compressor. an oil separator including a chamber configured to receive refrigerant from an air conditioning system; a heat exchanger, which also functions as a compressor oil separator, disposed within the oil separator; a compressor including a low pressure side fluidly connected to the chamber and a high pressure side fluidly connected to the heat exchanger; a compressor suction conduit and a compressor suction hose being connected in series and connecting the chamber and the low pressure side of the compressor; a compressor discharge tube and a compressor discharge conduit being connected in series and connecting the high pressure side of the compressor and the heat exchanger; a compressor oil return conduit and a compressor oil return hose connected in series and connecting the heat exchanger to the compressor; a first flow line that is fluidly connected to an inlet of the oil separator and connectable to a source of refrigerant; a first valve disposed in the first flow line; a second valve disposed in the compressor oil return conduit; and a controller operably connected to the compressor, the first valve, and the second valve and configured to, in a preheating operation, operate the first valve to open to enable a predetermined amount of refrigerant to pass into the chamber of the oil separator; activate the compressor; operate the second valve to open so that a flow loop for the predetermined amount of refrigerant is formed between the heat exchanger and the compressor comprising in this order the compressor, the compressor discharge tube and conduit (124, 164), the heat exchanger and the compressor oil return conduit with the second valve and the compressor oil return hose; and subsequently commence a refrigerant recovery operation, wherein the controller is further configured to periodically initiate a compressor oil return process during the refrigerant recovery operation to return compressor oil collected in the heat exchanger to the compressor, wherein the controller operates the second valve to open and the compressor to generate a constant suction in the compressor oil return conduit, thus urging the compressor oil collected in the heat exchanger through the compressor oil return conduit and the compressor oil return hose back into the compressor.