Compact Flash Card not reading on iMac

For some reason my new iMac will not read my compact flash cards. I've tried two different multi-format card readers and neither work for the CF card yet the other slots on the card reader work perfectly such as my SD card and micro SD cards. Also, when I plug my CF cards into my Windows machine they read perfectly. My camera (Canon 7d) formats my cards to FAT32 if that gives any insight into my situation. Any suggestions on what I can do to resolve this issue? I'm tired of plugging my camera into the computer every time I want to transfer pictures and Apple Support wasn't able to help me solve this either. Thank you.