@hfp777
Usualy, I measred the V ref and place that value into my code if I need a better read from the analog pins.
But you do have an open at the analog pin or it is connected ( by mistake ) to the + Vcc.
Connected the wrong way. Hum... A zener diode connect the wrong way will measure about 0.6 V - a standard diode voltage in a foward mode.
Like : + 5 ---- resistor ---- V analog -- anode -- cathode --- gnd = V analog = 0.6 V
The proper way to connect a zener :
+5 ----- resistor ---- V analog --- cathode --- anode --- gnd = V analog = 3.0 if the zener is a 3 V type.
Can you take a picture of your setup ? and post it. It may help.
My guess is : the LM335 is bad or a bad wiring somewhere to cause the "open".