Hello,
I have a Trane XE90 furnace that is 6 years old. The pilot is lit but it blows cold air and runs for long periods. I had it serviced including a fliter change in April and the technician said the high limit switch was stuck he got it to work but said it would not last very long. Can you tell me if this seems to be the problem again? And if so where it is located so I may replace it.
Thanks,
Buddy Silva

Sounds like the switch he messed with is defective. Just replace it.

Look for a pair of wires leading towards the combustion chamber. You may find pictures at https://www.askmehelpdesk.com/heating-air-conditioning/heating-cooling-maintenance-repair-troubleshooting-frequently-asked-questions-58313.html