I am working on a 1991 Janitrol by Goodman . This is a roof mounted Heat and A/c unit. The tenant is having a problem with heating. (EXAMPLE) When the thermostat is set for 63 degrees the unit operation is good except it will heat up to 64 then it shuts off . Then after about one minute the blower fan comes on again and runs for about one minute. The temp did not drop to warrant this to happen. I replaced the fan/limit switch in hopes this would repair but it still happens. What could the problem be?