Data Validation for a field formated as text that must show Numbers Only with a length of 4

[USAMax]

I thought this would be easy but it is not working. In Data Validation I choose Allow Custom and this formula:

=AND(ISNUMBER(RC),IF(LEN(RC)>4,LEFT(RC,4),IF(LEN(RC) > 0, RIGHT("0000" & RC, 4),"")))

Everything I enter fails.

Examples of what I expect.

Out In
0004 4
0023 23
0548 548
4964 24964

Note: For alignment I put the output first.

THIS SHOULD WORK!

 

[USAMax]

I did discover one thing, as the cell if formatted as TEXT the ISNUMBER will fail so I had to change it to ISNUMBER(RC + 0) to get this portion of the formula to work.