Flow control valve for injecting oil into an air conditioning circuit

An air conditioning service system, comprising:

• an oil receptacle configured to store an oil;
• a solenoid valve configured to selectively allow the oil to flow from the oil receptacle into an oil injection line;
• a coupling port in fluid communication with the oil receptacle through the oil injection line when the solenoid valve is in an open condition;
• and
• a flow control valve including a chamber with an inlet and an outlet, the inlet in fluid communication with the oil receptacle when the solenoid valve is in the open condition, and the outlet in fluid communication with the oil injection line when the solenoid valve is in the open condition,
• wherein the flow control valve is configured such that, for a given pressure difference between the inlet and the outlet, the oil flows from through the flow control valve at a flow rate that is independent of a viscosity of the oil within a predetermined range of viscosities.