REPLACE Operator -

I have a column of zip codes. Some zip codes have letters instead of numbers in the last two or three placeholders. I am using the REPLACE operator, selecting [A-Z] replace with 0 (zero). When I run this, I do not see zeros. The letters are gone but any placeholders at the end of the 5 digit zip codes are now blank, instead of zero.  - Sincerely, RMforDummies