My central heat and air keeps freezing up what should I do to stop it

Make sure that the intake air filters are clean. Dirty filters is probably the #1 reason an a/c freezes up in the summer. Also high humidity overnight when it is a tad cooler can also cause this to happen. I had an a/c in South Florida that was a totally outside unit and every spring or fall when the temp outside at night would get lower than 70 degrees and high humidity my a/c would freeze up. Invariably it was a dirty filter.

Bad circulation,dirty filter closed off supply vents,, blocked return vents,low on freon,just a few more to mention