Hello William,
If you have enabled Full Client Isolation on a WLAN, the Restricted Subnet (ACL) gets automatically applied on this WLAN and blocks access to all internal network devices, if you would like to allow access to certain devices like printer's you have to configure the Restricted Subnet available under Configure > Guest Access > Restricted Subnet. Here you will have to enter the IP address of the device you want user's to have access with a subnet of /32. For example if the IP address of the printer is 192.168.15.65, to give access you will have to enter 192.168.15.65/32 , this implies that all host bits need to match to allow access .
All the best.