When I turn on air conditioning black smoke comes out of the vents from under the dash, fan does not work, no smoke from engine bay on renault safrane 98 model

Is this a diesel engine?

Your controls are vacuum operated. Make sure that there is vacuum present...if not find the disconnect. Or, the vacuum "motor" that controls air direction has failed or is stuck.

assuning there is nothing major wrong, get some forte injector and use it as recommended. I once had a renault laguna diesel fail an MOT test, a roadworthiness test that is, on emissions...it was absolutely chucking out black smoke but the engine ran well. I put 2 bottles of injector cleaner in the half full tank and went out for an eighty mile drive revving the engine in the lower gears. I returned to the testing station an hour and a half later and the engine was running perfectly.
Alternatively, assuming the engine runs well but is just a little smokey, have it terracleaned, this will remove most of the carbon deposits from the engine/exhaust and should increase the life of your engine simultaneously improving fuel economy

blown head gasket --cracked head --or damaged engine block blue smoke is oil being burnt and the milky gunk is coolant/water mixing in with the oil

air direction gate is disconected . disassemble the heater assembly under the dash and reconect it

It is most likely the temp door actuator motor in the dash the dash has to be removed to repair the problem.

Its the Black vacumn pipe that will of cracked etc-look for the small thin black pipe that runs from left of engine bay and goes behind air box and top of engine-its a sod to replace but takes an hour or so!! Good luck..

u have a loss of engine vacuum to the dash control that moves the actuators that change the air flow around to the diff locations of the dash. Start at the engine supply hose and work backwards, the vacuum line comes in on the passenger side from the engine bay, it is under the dash along with other plastic vacuum lines the supply line is black, u will need a MITYVAC brand tester to check the vacuum supply to the diff vacuum actuators in the dash.

Find Someone else,
Have Them Replace The Fan Selector Switch,
There Is Only 1 Fan In The System, Since You Can Select Between Defrost, Dash, Floor,
But Cannot Control Fan Speed/Shut-Off Fan.
I Would Replace The " Fan Selector Switch" Installed In Your Heater-A/C Controller Unit
Mounted In Your Dash.
Take Care God Bless

Have you checked the diverter doors under the dash??
It sounds like a vaccum hose may have fallen off your vent controller.
I have had similar problems and found that the air WAS moving, but it was all going up through the defrost vents at the windshield.
A quick check of the vac. lines showed that one under the glove box was pulled off.
with the engine running, try setting the air settings to all the options ( vent/floor/defrost..etc..)
See it you can feel or hear the diverters moving under the dash..