The protective coating on the compressor blades is what I think is the cause of that smell.
Unfortunately theres not much that can be done as all air for bleed services is tapped off downstream of the compressor, & the fact heat will amplify the fumes/odors.
Jet fuel is kerosene, smells similar to deisel.
Aircond pack uses pressured air from the engine for pressurisation (unlike cars using an electric fan to pump air out the vents).
Its actually a much better system than using a refrigerent type.
In an aircraft, the air is constantly renewed with conditioned, outside air.
Airconds in buildings & vehicles run efficiently cos they are conditioning the already conditioned air (recirc).
Heres a speil of what goes on.
The air leaves (bleed air) the engine diffuser (after compressor stages/immediately before burner section) under pressure @ over 260degreesC.
It is then delivered as is, to the aircond pack/s & other bleed services - ie. ice protection, eng starting.
There aircond pack cools this hot/high pressure air through 2 stages: 1- primary heat exchanger - ram air being the cooling medium, 2- air cycle machine - utilising remaining heat energy of the partially cooled air to spin the turbine (drives a fan to cycle ambient air over heat exchanger), thus cooling the air further.
From here it travel through a water separator, to a mixing chamber (where hot bleed air is added as required to maintain set temp) before being delivered to the cabin as conditioned air.
I guess I got a bit side tracked there, but hope this will give you a better idea of where that odor could be coming from