Sagging with ABS printing

bed is set to 110c
extruder is set to 245c
extruder fan is set to automatic cooling of cold-end
Printing onto glass with hair spray as adhesive.
printing with 100% infill

have done a 2 hour print and left it, when it was 50% it was perfect, perfect lines, perfect infil.
but...
when i get back after the full 2 hours, the corners have stuck up and side are sagging and drooping, it bowed and looks horrible...

does anyone have a suggestions?
should i add a print fan? directing air onto the print job???.

lowering ABS extrusion temp? (it is @ 245c)

For abs printing:

Kapton + acetone and little ABS.
Enclosure
Heated bed at 110°C during all the print.
No fan at all.

for example of printing with that method:
http://forums.reprap.org/read.php?279,401375

In ABS and no warping and no cracking...

does that mean no fan for cold end of extruder?

If the fan does not reach the printed parts it is ok, if it does you have to adjust the airflow.
Depending on the size of the print you might even need a heated chamber to print ABS.

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