asp:TextBox - Is there a way to OnTextChanged working even after setting visible=false?

Question

Is there a way to OnTextChanged working even after setting visible=false? I have a legacy asp page that has a number of postbacks and refreshes. I'm using this text box as a session variable since the equivalent variable in the code behind can get unexpectedly cleared during one of the many refresh events. This textbox can be changed because of a wanted ajax auto-complete call and I need to know when it does.

<asp:TextBox runat="server" Visible="false" ID="txtClientId" CssClass="text-box" AutoPostBack="True" OnTextChanged="OnClientIdChanged" />

You are correct, it's my ajax to update the field that is failing while the text box is not visible. I put in the variable "t" to look at what I just set and it is failing. Is my only option to enable visibility, set the value, then disable visibility?

function SupplierSelected(source, eventArgs) 
{ 
    var client = JSON.parse(eventArgs._value);
    $("#ctl00_cphMasterPage_txtClientId").val(client.Id); 
    var t = $("#ctl00_cphMasterPage_txtClientId").val();
}