Central heat and air system won't shut off

Question

When I turn the ac or the heater on it wont stop running and the heat pump outside dose not shut off either. I have replaced the thermostat and shut it off for about too weeks bur it still funs constantly running and if I have it on cool the coils freeze up in the unit and its starting to bug the heck out of me and I want to get it fixed so it dose not cost me in the long run can you help