Remote control When we press the power button on the remote, the timer light comes on. The AC does not function unless we use the manual power switch on the AC itself. We never use the timer. Do we need a new remote?

I would try a new remote first, if that doesn't correct the problem you have an issue with the main circuit board in the AC unit.

If pressing the power button on the remote only activates the timer light and the AC won't turn on unless you use the manual switch on the unit, it usually means the remote is sending the wrong command or the power button's internal contact is failing. Sometimes the remote slips into timer mode due to a stuck key or weakened batteries.
Start by replacing the batteries and cleaning the buttons, especially the Power and Timer keys, since dust or wear can cause the remote to send the wrong signal. Also reset the AC by unplugging it for 2-3 minutes. If the remote still triggers only the timer light, the IR signal for power is likely faulty, and replacing the remote is usually the simplest fix.
For guidance on remote programming and IR behavior, this universal remote reference guide may help: https://manualslibraryy.com/radio-shack-15-2147-universal-remote-control-user-manual/