agree with Peter and Clive - take out the CC before you test anything. CCs introduce severe internal aberrations that can influence the image if the CC is not exactly on and aligned with the optical axis and with the right spacing.
If you still find astigmatism with the CC out, then the main optics are suspect (mainly the secondary mounting ?).
However, if the optics are OK, suggest putting the CC in and then laser collimating through it to get as close as possible to the proper CC alignment.
Re the fan, FWIW, I find that having a fan running all the time helps a lot with clearing the layer of warm air from the mirror surface and getting rid of tube currents. Used to do planetary imaging and it was fascinating to watch the resolution improve within a couple of seconds of switching on the fans. In rare perfect conditions, the fans seemed to introduce enough turbulence to cut the finest detail, but most of the time the resolution was definitely better with fans on. For DSO imaging it always seems better.
Cheers Ray
From
https://www.telescope-optics.net/sub...htm#correction
"For complete correction of a paraboloid, more complex correctors are required. In general, they need to have three (or more) single lenses, or two or more achromatized doublets. The lenses are more widely separated, creating more degrees of freedom, so that combined aberrations can be brought to a negligible minimum (for instance, the Paracorr-like corrector corrects coma with the front achromat without inducing spherical aberration, but it does come at a cost of inducing enormous astigmatism, then corrected with the rear achromat - something that cannot be done without widening lens separation). Examples of this advanced corrector type are TeleVue's Paracorr and Wynne triplet."