Thermo King V500 20 defrost issue

[tkfreezer]

I have a defrost question, i purchased a used truck box with this unit intact ( V500 20 ) i am using it as a stand alone freezer. Unit works great on electric power, however for some reason it wont go into auto defrost. I can however initiate a manual defrost. Setpoint is 20F, the evap does freeze up at least once per day. Does anyone have any ideas as to what the problem may be.

[cadwaladr]

What type of in cab controller is it do you have a picture?

[tkfreezer]

M13
Thank you for your reply

[cadwaladr]

Do you have a picture of the controller?

[cadwaladr]

If it's the one I am thinking of try holding the select button while it's running the select button is the top middle the one that's a circle of arrows,hold it until DIT comes up release it and change the interval time with the up/down cursors then press enter which is the equals cursor

[IRMechanik]

Does the cab command have three buttons (on/off, defrost and setpoint) and the setpoint control is a knob? Pretty sure that's the M13. The defrost interval on those is changed with a knob on the interface board.