I have a 5kw A/C -elect heat unit (York) That is being exteremly stubborn. It seems that the t-stat will not control the unit condensing unit runs constantly and the blower will not run at all unless I jump the R and G terminals together on the control board in the unit. The bord has been replaced and the t-stat as well. HELP!?

The first thing you need to do is wring out the wiring... disconnect the thermostat. Did you replace the board? Is it installed correctly? Verify the wires are going where they are supposed to, and veryify the accuracy of the color codes. Check all connections for tightness. Was the board replaced because for these problems... how about the t-stat? If the problems continued after the board and t-stat were changed, you have a wiring problem. Start with the wiring.