How to binding an object property in a userControl?

[Fenix]

Hi, i'm having a rough fight with WPF and its Binding system. I just wanna bind a property of an instance called HPP, this property is pressure and this object exist in MainViewModel, so in MainWindow.xaml a have this:

<componentes:SetComponent x:Name="HPP_Trip_Route" Grid.Row="1" Grid.Column="1" VerticalAlignment="Top" Title="TRIP" VariableValue="{Binding HPPRoute.Pressure}" Unity="PSI" Loaded="SetComponent_Loaded" FSizeTitle="24" FSizeVariable="36" FSizeUnity="14"/>

In SetComponent:

<TextBlock x:Name="ValueSetComponent" Grid.Row="1" Text="{Binding VariableValue, RelativeSource={RelativeSource AncestorType=UserControl}}" FontSize="{Binding FSizeVariable}" HorizontalAlignment="Right" VerticalAlignment="Bottom" Foreground="#FFFFFF" Margin="0, 5, 0, 5 "/>
Dar clic y arrastrar para mover

In MainWindow.xaml.cs:

public partial class MainWindow : Window, INotifyPropertyChanged
    {
        private readonly Variables GV = Variables.GetInstancia();
        private MainViewModel _mainViewModel;
        public MainViewModel MainViewModel
        {
            get { return _mainViewModel; }
            set
            {
                _mainViewModel = value;
                OnPropertyChanged();
            }
        }

        public MainWindow()
        {
            InitializeComponent();
            GV.MainViewModel.StartAssign(GV);
            MainViewModel = GV.MainViewModel;
            GV.MainViewModel.MainWindow = this;
            DataContext = MainViewModel;
     
        }
        public event PropertyChangedEventHandler PropertyChanged;

        protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }

I tried with RelativeSource without success. If i create a variable in MainViewModel it works. Any help?

[Dinko]

I made a project from the code you have given. It looks like everything is working fine. Try this attached project and tell me is it working properly and is the setup right.