Thank you all.
I have also heard that 90% APUs are Honeywell, who bought Garret. The B757 APU use the Fairchild Metro II engine (Garret TPE331 now APU Honeywell 331). When I was said that, I was riding the CRJ200. I don't remember the CRJ APU manufacturer but every time packs was switched on, the APU EGT indication went into the red side for an instant. That probably was due to not having a system such as in bigger crafts with variable angle vanes for the bleed output. That also could be the reason for the cycle consideration of such a thermal shock.
Tailwinds