As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ON FLIGHT 3653, CREW REPORTED DURING TAXI OUT WITH APU BLEED SUPPLYING THE PACKS A HAZE IN THE COCKPIT AND CABIN WAS NOTED. AIRCRAFT REMOVED FROM SERVICE. REMOVED AND REPLACED LT HEAT EXCHANGER AND LEFT ACM IAW EMB AMM 21-51-02 AND 21-51-03. OPERATIONAL CHECK GOOD. AIRCRAFT RETURNED TO SERVICE.