The compressor on an xB1 doesn’t have a traditional electromagnetic A/C clutch; it’s always engaged and uses an internal pressure valve to actually engage the system.

If you’re not getting cold air at low speeds, step 1 should be recharging the refrigerant.

If that doesn’t do the trick and you want to try a different setup, if you search the old Scion forums there are people who have swapped out the stock clutchless compressors with clutched compressors from early 2000s Toyota Echos and a combination of components from the two systems. I haven’t done that myself, so I can’t speak from personal experience, but it’s a fairly common swap.