No cold air from a/c

My buddies 2006 dodge Durango has a good blower motor a/c compressor does not kick in with switch on light in dash says its working yellow light .All fuses ck. good , relays ck. good. no power from plug to compressor my friend and brother said something about a low press. switch the motor works fine when you jump it from battery but no cold air any ideas how much this switch is and where is it located .. Thanks for any help very much appreciated !!!!