1. The wires are reversed and it is actually the active bearing that is running hot. How many probes are in each bearing? Switch to the installed spare. Do the thrust probes confirm that the rotor is thrusting inactive?
2. The rotor is thrusting hard inactive because it is operating at excessively high flow. Where is the compressor operating relative to design flow?
3. The coupling spacing was set incorrectly and the coupling is running in hard compression or tension, depending on the normal direction of thrust.
4. The normal direction of thrust is different than expected. We have centrifugal compressors that normally thrust toward the discharge. The technician that set up the instrumentation assumed that the compressor would thrust toward the suction or toward the coupling because that is all he has ever seen. Confirm the normal thrust direction with the compressor manufacturer.
Unless you provide some details about the compressor, service and history (new machine, just overhauled, sudden event mid-run, etc.) the best we can do is offer wild guesses. If you want us to spend time analyzing your problem, you need to spend some time providing details and background.
A restricted balance line would typically result in high thrust in the active direction. But, once again, without additional information, I can only give a guess.
