I have successfully added thermistors in the field. The compatibility with R123 is a must on epoxy/varnish. If motor rewind is chosen, I would only have Trane rewind a Motor for use on machines utilizing R123. Have you confirmed motor winding integrity?

I did some in the field many years ago on a semi hermetic Carrier Centrif , dropped the back off the motor and tied some new thermistors in that we got along with varnish and cloth ties from a local motor rewind place we used, installed them and used the existing failed terminals to route the wiring back out, put them back on and gassed it up and ran fine. You could also try external sensors either on the motor body or motor cooling exit pipe if it has one.

Thanks for the responses. We advised the customer to allow us to remove the motor and send for total rework to fully guarantee the outcome. Not looking for a quick way out but true Customer Service sometimes demands a proper risk assessment.