ruud furnace problem
On most models of Rheem/Ruud furnaces, if there is a limit open it will not do anything. Turn your thermostat to the heat mode, use a votmeter on A/C volts. Locate your limits and put one of each of your probes on either side of your limit. If you read voltage that is the limit that is open. Most are resettable, but if it is not you should be able to go to a dealer and get a new one. They will tipically range from 12-25 dollars.
Good luck and let me know if that does't work.