I have a Clare OLB 503RD Furnace with Coleman Central Air Unit. The AC Unit comes on outside and the furnace fan shuts down. AC freezes up. Is there a relay or motor control on the fan that has failed

Yes it is possible the fan relay is defective. In the mean time try to turn the thermostat blower control to run all the time. That may or may not work but you will still need to find the problem.