Javascript vairables empty unless I debug code - php

Question

I have a function which makes a ajax call and gets a list of vehicle make.
var car_make_list_target_id = 'car_make';
var make_year_list_select_id = 'years';
var car_model_list_target_id = 'car_model';function get_car_model(){
var car_model_initial_target_html = '<option value="">--Select Model--</option>';
//Grab the chosen value on first select list change
var selectvalue = $('#car_make').val();
alert('first alert ' + selectvalue);
var yearvalue = $('#' + make_year_list_select_id).val();
//Display 'loading' status in the target select list
$('#' + car_model_list_target_id).html('<option value="">Loading Car Models</option>');
if(selectvalue === ""){
//Display initial prompt in target select if blank value selected
$('#' + car_model_list_target_id).html(car_model_initial_target_html);
} else{
//Make AJAX request, using the selected value as the GET
$.ajax({
url: 'get_model.php?make=' + selectvalue + '&year=' + yearvalue,
success: function(output){
//alert(output);
$('#' + car_model_list_target_id).html(output);
},
error: function(xhr, ajaxOptions, thrownError){
alert(xhr.status + " " + thrownError);
}
});
}
I also have a php if loop to see is session isset. Now I want to display these values within the drop down list if the session is set.
if(isset($_SESSION['vehicle_info'])){
echo '<script>'
.'$("#states option[value=' . $_SESSION['vehicle_info']['state'] . ']").attr("selected","selected");'
.'$("#years option[value=' . $_SESSION['vehicle_info']['year'] . ']").attr("selected","selected");'
. ' $("#years").prop("disabled", false);'
. ' $("#car_make").prop("disabled", false);'
. ' $("#car_model").prop("disabled", false);'
. 'get_car_make();//This works'
. 'get_car_model();//This does not work unless I debug javascript'
. '</script>';
}
The issue is unless I set a breakpoint within the get_car_model on the following lines
var selectvalue = $('#car_make').val();
alert('first alert ' + selectvalue);
the var selectvalue is blank, but if I leave the breakpoint it will alert the value of the option and will display correctly. I have been beating my head for the last 4 hours and I have not been able to figure this out. Is this normal browser behavior or am I missing something? Any input will be great.