http://stackoverflow.com/a/27325768/1678614

HTML

<div ng-app="app" ng-controller="ctrl">
    <p>The text input will clear when you select a new type.</p>
	<input type="text" ng-model="text">
	<select ng-model="type" ng-change="clear()" ng-options="type.id as type.name for type in types">
		<option value="">- Choose Type -</option>
	</select>
</div>

JavaScript

angular.module("app", []).controller("ctrl", function($scope){
	$scope.text = "Hello";
	$scope.types = [
		{id: 1, name: "Type 1"},
		{id: 2, name: "Type 2"}
	];

	$scope.clear = function() {
		$scope.text = '';
	}
});