As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
On taxi out had double pack trip and cooling fan CB popped. Ran C/B reset procedure and pack trip off procedure. Re-continued taxi and had double pack trip and cooling fan control breaker popped again and had right duct overheat light.ACTION TAKEN:Removed and replaced left isolation valve ops checked normal.