What is a red flash condition on a residential YORK gas furnace?

It would help to know the model and thelevel of efficiency. Models more efficient than 87% can be vented via PVC pipe, is yours? If so, chcek for a small black or clear tubing inside the control area. This tube makes a complete loop or at least a pronounced dip. It is a condensate trap and must be clear. Pull tubing off at both ends and blow air through the tube, now replace. Any better

There should be some sort of service legend/label explaining the status codes. Check inside front/blower panel.