Have you properly configured the pin for INPUT (eg set the TRIS for that pin)?

Have you DISABLED the COMPARATORS that use that pin?

Have you ENABLED that pin for ANALOG input?

What EXACTLY makes you think that RA4 is Open Collector? Some dubious second-hand information that you got off the internet? Just because RA4 is Open Collector on one PIC, doesn't mean it is on another... so find out if that statement is true or not.

And if it was Open Collector, what has that got to do with using the pin for INPUT?

There is ONLY ONE definitive source of reliable information for any PIC chip. That is the manufacturers DATASHEET downloadable from Microchips website. Go do it.