An oil balancing system for a multiple compressor system, the oil balancing system comprising: a first compressor; a second compressor; an oil equalization line disposed between the first compressor and the second compressor; a first valve in the oil equalization line; an oil level detection system configured to generate a first signal corresponding to a first oil level in the first compressor and a second signal corresponding to a second oil level in the second compressor; and an oil balancing module configured to use the first signal and the second signal to diagnose an oil imbalance between the first compressor and the second compressor, and to apply corrective action, whereby the corrective action comprises: a) sending control signals to change the operating speed of one of the first compressor and the second compressor, and operating the first valve in a way that eliminates or reduces the oil imbalance; or b) sending pulse width modulated control signals to the first solenoid valve in a way that can closely match an oil transfer between the first and second compressors; wherein the oil level detecting system is configured to use the first signal to determine whether the first compressor operates in an acceptable mode or an unacceptable mode based on a first predetermined unacceptable value for the first signal, and to use the second signal to determine whether the second compressor operates in the acceptable mode or the unacceptable mode based on a second predetermined unacceptable value for the second signal; wherein the oil level detecting system is configured to use the first signal to determine whether the first compressor operates in a warning mode based on a first predetermined warning value for the first signal, and to use the second signal to determine whether the second compressor operates in the warning mode based on a second predetermined warning value for the second signal; and a self-learning module configured to create a record of time spent in an acceptable mode, warning mode, and unacceptable mode for each of the first compressor and the second compressor, wherein the self-learning module alters the corrective action of the oil balancing module based on the record. a first compressor; a second compressor; an oil equalization line disposed between the first compressor and the second compressor; a first valve in the oil equalization line; an oil level detection system configured to generate a first signal corresponding to a first oil level in the first compressor and a second signal corresponding to a second oil level in the second compressor; and an oil balancing module configured to use the first signal and the second signal to diagnose an oil imbalance between the first compressor and the second compressor, and to apply corrective action, whereby the corrective action comprises: a) sending control signals to change the operating speed of one of the first compressor and the second compressor, and operating the first valve in a way that eliminates or reduces the oil imbalance; or b) sending pulse width modulated control signals to the first solenoid valve in a way that can closely match an oil transfer between the first and second compressors; a) sending control signals to change the operating speed of one of the first compressor and the second compressor, and operating the first valve in a way that eliminates or reduces the oil imbalance; or b) sending pulse width modulated control signals to the first solenoid valve in a way that can closely match an oil transfer between the first and second compressors; wherein the oil level detecting system is configured to use the first signal to determine whether the first compressor operates in an acceptable mode or an unacceptable mode based on a first predetermined unacceptable value for the first signal, and to use the second signal to determine whether the second compressor operates in the acceptable mode or the unacceptable mode based on a second predetermined unacceptable value for the second signal; wherein the oil level detecting system is configured to use the first signal to determine whether the first compressor operates in a warning mode based on a first predetermined warning value for the first signal, and to use the second signal to determine whether the second compressor operates in the warning mode based on a second predetermined warning value for the second signal; and a self-learning module configured to create a record of time spent in an acceptable mode, warning mode, and unacceptable mode for each of the first compressor and the second compressor, wherein the self-learning module alters the corrective action of the oil balancing module based on the record.