Recently my '93 Altima's temperature gauge while driving has stayed down on the cold mark and will gradually go the the half way mark but never going past that, also when the defrost is on it blows out cold air...but if you turn it to heat and use the vents warm air will come out eventually getting hot...all fluids have been checked and filled.....today i drove it to work drove just fine, several hours later when I hoped in to drive home it would not start (it would turn over but not connect or catch) I am wondering if these problems are connected or do I just need to replace both thermostat and rotor cap....Also i noticed that there was a clicking sound coming from the dashboard temp controls if you moved it either way too far you would hear it. Thanks again for all your help and is greatly appricated

I doubt they are related, you wont get heat until the car is warmed up, don't know about the dashboard clicking. is it cranking slowly? any driving symptoms b4 this happened? if it takes literally forever for the car to warm up the thermostat might be stuck open, if not dont worry about it. if it cranks over ok then it could be one of the fallowing problems, fuel,air intake, or ignition. a good mechanic could probably fix this.