Volvo: 1990 Volvo 240, radiator shop, clutch fan

Question
How often should the timing belt be replaced? Should it be done if the car is running fine, as preventative maintenance? I have 149,000 miles. What about the water pump? I don't see it leaking - just wait until it goes? Also, if the car  starts to overheat ONLY when the AC is on AND you are standing still, is that the clutch fan?  

Answer
Larry,
Replace the timing belt every 50K or 5 years. Choice is yours on the pump, personally I would replace it. Overheating could be the fan clutch a partially clogged radiator, improperly working temp compensation PC board in the dash cluster. When he car is overheating place your hand behind the fan close to the t/stat and feel if it is drawing a lot of air. Test it cold and hot to compare how well the fan draws the air. Pull out the radiator have a radiator shop test the flow. As long as the radiator is out change the t/stat. Lastly if gauge still goes up use a temp gun and read the temp at the t/stat to see how hot it is. If the temp is not above 200 degrees replace the comp board in the cluster.