2007 Skoda Roomster the problem is that when the heater fan on the engine loos the power, that only come up whel

could do with more information on this problem but when your air con is on the engine has to work harder to drive the air con compressor this is driven of the engine there could be a fault with the compressor but i would make sure that there are no engine problems with your car i would also check the battery and have the alternator charge rate checked