2000 focus temp gauge fluctuate from norm to red when travelling at speed ..but all coolant levels ok and not loosing anything and fan working.

Check the coolant level. Sometimes when the coolant level is low, it will cause gauge fluctuations like you suggest, since air is getting into the cooling system. When air is in the system, it causes the thermostat to open and close frequently resulting is wild temp gauge swings.

Watch the temp gauge when the electric radiator fans come on. The temp sensor that controls when the fan comes on may be faulty.

YOU NEED BLEED COOLANT SYSTEM.CHECK COOLANT LEVEL IN RADIATOR.ADD MORE DEXCOOL UNTIL COOLANT LEVEL IS CLOSE TO RADIATOR SPOUT.CRANK ENGINE LET IDLE UNTIL TOP RADIATOR HOSE GET HOT.WATCH TEMPERATURE GAUGE.IF TEMPERATURE GAUGE START RISING TO HOT ZONE.TURN OFF ENGINE.LET COOL DOWN.USE LARGE RAG SLOWLY OPEN RADIATOR CAP A LITTLE AT A TIME UNTIL ALL PRESSURE RELIEVED.REMOVE RADIATOR CAP.ADD MORE COOLANT.CRANK CAR AGAIN LET IDLE UNTIL TOP RADIATOR GET HOT.KEEP EYE ON TEMP.GAUGE ALSO.WHEN TEMP.GAUGE STOP CLIMBING.YOUR COOLANT SYSTEM BLED.WHEN DONE LET CAR SET A WHILE CHECK COOLANT LEVEL.ALSO FIRST THING IN THE MORNING CHECK COOLANT LEVEL AGAIN.AND BESURE ADD COOLANT IN THE OVERFLOW JUG TO THE COLD MARK.DONT OVER FILL THE COOLANT RESERVOIR JUG.WORK SAFELY DONT GET SCALDED.

first thing to check is your coolant level. a lot of fluctuation will occur if the coolant level is low. if it is, be sure to find the leak to avoid engine damage. other causes can be plugged radiator, faulty thermostat, etc. but start with the coolant level.

Because you have done so many repairs already I would most likely say that the gauge is defective. I would use a manual temp probe and probe the coolant temp after the car has reached operating temp. Coolant will be between 180- 230 degrees. If coolant temp checks out and you can see coolant moving in radiator and the vehicle does not overheat then you will need either a gauge or a coolant sensor. To locate the sensor it should either be mounted in the thermostat goose neck housing or the intake manifold.

When on the highway the wind blown through the grille naturally cools the rad coolant. While stuck in traffic the radiator fan will intermittantly cut in to prevent over heating, thus the fluctuations in the temp. gauge.

Look for a loose connection to the temperature sender unit on the motor.
If all connections OK, you may need a new temp sender unit.

you may have a stuck thermostat,if all fans are working then just flush out radiator and replace
thermostat.check for any coolant leaks and check coolant level after few days

Is the blower fan for the heater going on, but only cold air? If the fan is working, but no hot air situation, 1st check the coolant level, if it's low, the coolant won't flow thru the heater core, so little or no heat. If level is ok, what does the engine temp gauge indicate? Is the engine running normal temp range, cold, hot? Let me know answers to these questions so I can help u.

the ac work that you had done wont do that,start the car ,let it run for a little bit,with a glove on,or a rag squeeze the top radiator hose ,once its full of pressure,when you see the fan go on it should make the hose soft,meaning the thermostat opened,if not change the thermostat,if the fans go on and your thermostats open,you have to have the radiator