2001 blue light stays on unless A/C turned on

My blue temperature at one time started blinking -- found some info online about adding a specific amount of distilled water and coolant -- added it and when the engine was warm the light went off. Also discovered that letting the car warm up for a couple of minutes before driving helped as well. Now, the blue light stays regardless of how far I drive or for how long unless the A/C is turned on. Then it will go off.

Help? I'm not rich but do have a son that is a whiz at repairs -- if he knows what to repair.

this really sounds like a weird wiring issue because the a/c and the blue temp light on ur cluster shouldnt affect each other, theyre two completely different circuits for the a/c controls and for the temp sender. is your check engine light on? if it is, its possibly for a temp sender implausable signal fault, and in that case you would just need to replace your coolant temperature sensor. either way, as long as it isnt some screwy wiring thing, a temp sender and a thermostat should take care of this.