Car lose coolant only with air conditioner running i can drive it all day without air conditioner and don't lose any.Please advise

Yeah, replace the coolant and find out where it's leaking and fix it. You can destroy the engine by running it without coolant, it gets too hot and everything expands and soon the pistons will seize to the cylinder walls and your done. Then must rebuild. Fix it now while it's still running well.

Good idea is to drain the coolant from your radiator, then replace the hose that is leaking and then fill with coolant to the proper level. Drive your car and have heater running to remove any air in the system.

run fault codes and find out which sensors are faulty. The loss of power indicates that it is in limp home mode . Check oil level and coolant level at the radiator cap.

You have air trapped in system , change thermostat , bleed air from system , let it run hot while adding coolant with blower full blast on all front and rear heaters .

indicates that the fan is not drawing air through the radiator at idle or low road speeds
If viscous fan hub --replace it
if electric fans check
coolant temp sensor
2 fuses , relay . fans . ECM

To start with, you are talking about the temp gauge. The thermostat is in the engine.
The coolant system could be low or have air pockets and still look full.
First thing I would check is the cooling fan, then the coolant level.

As crazy as it sounds, I don't see why not. Based on my limited knowledge of a 2002 L200, the power steering is run off the back of the camshaft and the water pump is driven by the timing belt. The only things the serpentine belt runs are the A/C and alternator. Obviously you won't make it very far running without an alternator, but at worst you kill your battery. Serpentine belt on a 2.2l 4 cylinder 2002 L200 has nothing to do with the water pump or power steering pump.

you may want to try finding a tube of graphite usually sold at wal-mart in the automotive section that will clearly state it is for coolant systems; the graphite will build up around the hole and usually fix the leak; if not, consult your local mechanic to find the root of the problem... most likely a leaking coolant line, hose or radiator

make sure your plugs and wires are in good condition.also fuel and air filter.the engine has to be well tuned up.because air conditioner compressor put a little load on engine.if engine is not well tuned.the AC will pull it down.cause it to lose power and run rough.

If compressor isn't kicking in, check the connector atop the a/c accumulator, beside the coolant recover tank, in the engine compartment. That connector is atop a black bottle, and the connector goes to the low pressure switch. These switches do fail, and you can jump a wire across the connector terminals to see if the compressor comes on (engine running). As this circuit provides part of the ground path from the compressor clutch, if the switch is open, the compressor will never turn on. If the switch is failed, it can be replaced without opening the a/c system. Just disconnect the connector, unscrew the switch, replace it, and reconnect the connector.