Temperature gauge always reads lowest

Hi,

I have a 99 Durango with a temp gauge that doesn't move. I drive it for a 40 minute commute. There is some heat coming out of the blower, although I am not sure it if is really heating up properly.

The gauge stays at the lowest temp. Not sure if it could be the sending unit or whatever.

There is coolant, full, in the cooling system. Is this a case of a bad sensor or maybe something more serious?

Thanks in advance,

Mike

you say that there is heat coming from you blower. This could be due to a sticking/broken heater blend door...does your ac also blow warm