Dodge Ram 1500, air will blow when switch in high position.

You replaced the resistor and WHAT relay? The blower motor circuit on a 2007 Dodge Nitro does not use a relay.

The blower resistor gets it's power from the A/C - heater control unit.

If you check for voltage at the blower motor resistor connector (Key on, relay disconnected), the DARK BLUE/GREY wire should be hot when the control switch is on HIGH. The DARK BLUE/VIOLET wire should be hot with the switch in the MEDIUM 2 position.The DARK BLUE/ORANGE wire should be hot with the switch in the MEDIUM 1 position. The DARK BLUE/BROWN wire should be hot with the switch on LOW.

If any of these are not as stated above, then you either have a bad A/C - heater control unit, or faulty wiring between the control unit and the resistor.

Blower motor resistor needs replacing. Follow wires from blower motor to connector, which should be the resistor. Usually in duct work, held in by 2 small screws.

sounds link the servo door has either broke off or is not working and it is stuck in a closed position

replace switch

sounds like your cables in the selector switches may be loose or blocked

You may need to add coolant to the cooling system, That is considered secondary and if the level is low the engine gets coolant priority, after you add check it again soon, as it may get air locked and once you drive it it may go low again, if that isn't the problem then you may need a thermostat is the engine warming up?

Have you checked for freon leaks. It sounds like it's low and the pressure switch drops out. Try adding freon.

YES THE AC SYSTEM IS LOW ON REFRIDERENT. U HAVE A LEAK SOMEWHERE.

change the blower resister module,if this doesnt work replace the control head

By pass both pressure switches one at a time with small wire or a paper clip. If comperssor kicks on replace the swich that you bypassed.
if not it could be the fan clutch ot the compressor. Compressor runs about $400.00