Fuel Gage And A/c

[OAKTOWNLEXUS]

I HAVE 1990 LS400 MY FUEL GAGE THAT SHOWS HOW MUCH GAS I GOT IS STUCK IT ALWAYS SHOWS I GOT A 1/4 OF A TANK LEFT I HAVE TO KEEP LOOKING FOR THE RED LIGHT TO TURN ON TO KNOW WHEN I GOT TO PUT IN MORE GAS WHAT DO I HAVE TO DO TO GET THIS FIXED. AND ALSO MY CARS A/C DOESNT THROW OUT VERY COLD AIR AND IT STARTS TO HEAT UP WHEN I HAVE THE A/C ON AND THE CAR IS PARKED IF IM DRIVEN IN THE STREET I CANT TURN ON MY A/C CUZ MY CAR WILL HEAT UP WHAT CAN I DO TO FIX THIS ANY INFO WOULD BE MUCH HELPFUL THANX