Maintenance Manager reported Captain reactivated a deferred APU for ground cooling and did not request maintenance action to reinstate the MEL afterwards. The aircraft departed that station with no action.

Narrative

Captain reported aircraft was too hot to board passengers; conditioned air was INOP; and APU was on MEL; so he would refuse the aircraft unless he could reactivate the MELed APU briefly to cool down aircraft. I went out to talk to the Captain to get a clearer direction on what he wanted and he said he was going to turn the APU on to cool down the aircraft. We informed the Captain that the APU was on MEL for fire loop not testing and exhaust cone issues; and that would reactivate the APU from MEL. Maintenance Control was also trying to clarify whether this would even be possible without a fire watch. Went outside to APU to inspect and me being in Management; to call maintenance personnel for support; and control to figure out a course of action when I heard the APU fire up. No maintenance personnel was present in Flight Deck or Outside aircraft; no fire watch personnel was present; APU was placarded INOP; and MEL was complied with previously. I called my OM on duty to report this and see what steps I needed to take; or if he thought this was a compliance issue; and he told me it was out of our hands at that point as it had already been reactivated by the pilot. I then witnessed boarding of the aircraft with passengers (with a fire loop issue on APU) after the Controller told pilot he should not board passengers with the APU running that was deferred for that. Later the door was shut with APU still running; then APU was shut off and aircraft departed gate for flight. I feel the Pilot (whether it be the Captain or First Officer (FO) I cannot be certain) performed maintenance by reactivating a deferred item on MEL that could have caused a safety issue without maintenance or fire watch present. Maintenance was not asked to put APU back into placarded INOP status to continue to comply with MEL before aircraft departed. I felt I needed to report this; as I felt this was off compliance wise; and a grey area that I have not dealt with before. The Controller I was communicating with; including Operations felt the same way in communication with what was going on and with the Pilots.