By April 2017 only one of the 4 redundant coolant pumps for the silicon trackers was fully working, and repairs were being planned, despite AMS-02 not being designed to be serviced in space.
By 2019, the last one was being operated intermittently.
In November 2019, after four years of planning, special tools and equipment were sent to the ISS for in-situ repairs that may require four or five EVAs.
 Liquid carbon dioxide coolant was also replenished.

The repairs were conducted by the ISS crew of Expedition 61.
The spacewalkers were the expedition commander and ESA astronaut Luca Parmitano, and NASA astronaut Andrew Morgan.
Both of them were assisted by NASA astronauts Christina Koch and Jessica Meir who operated the Canadarm2 robotic arm from inside the Station.
The spacewalks were described as the "most challenging since [the last] Hubble repairs".
By April 2017 only one of the 4 redundant coolant pumps for the silicon trackers was fully working, and repairs were being planned, despite AMS-02 not being designed to be serviced in space. By 2019, the last one was being operated intermittently. In November 2019, after four years of planning, special tools and equipment were sent to the ISS for in-situ repairs that may require four or five EVAs.  Liquid carbon dioxide coolant was also replenished.
The repairs were conducted by the ISS crew of Expedition 61. The spacewalkers were the expedition commander and ESA astronaut Luca Parmitano, and NASA astronaut Andrew Morgan. Both of them were assisted by NASA astronauts Christina Koch and Jessica Meir who operated the Canadarm2 robotic arm from inside the Station. The spacewalks were described as the "most challenging since [the last] Hubble repairs".
Alpha Magnetic Spectrometer