Have an arc fault breaker that trips as soon as the switch is turned on to some can lighting in a bedroom.wall outlets are on the same circuit and work fine when a load is put on them.if I take the lamps out of the cans and turn on the switch it holds as well.could one of the thermal devices in the cans be causing this? Any help appreciated.
Thermal device could be causing problems, I wouldn't focus too hard on that just yet though, have you tried installing lamps until you find which lamp or luminaire seems to be giving trouble? Once you find one move that lamp to other luminaires to help verify if it is the lamp or the luminaire causing problems. I wouldn't rule out any potential bad connections at a socket either.
Lamp type could also be non compatible with the AFCI, like maybe some CFL's or LED's create a waveform the AFCI doesn't like, incandescents shouldn't give you this kind of problem though.