Compressor turns slow when motor is running

I believe they may make a different idler bracket to compensate for the change. You need a certain belt length for the Alternator and water pump to work properly at a given engine rpm. If you change the belt length, the alternator and water pump will turn either slower or faster than designed.

When on high speed the motor is running at it's normal speed.

When a slower speed is selected (mostly) there is external circuitry to reduce the current to the motor so it runs at a slower speed, though in some cases the motor could be specially wound for multiple speeds. The latter way is unlikely to be found in a cooker hood or extractor fan or other small appliance.

The fault with your appliance could be the switch or the current reducing circitry. It is only by delving inside and testing that the fault could be found.

pull the pulley off the compressor and replace the bearing in the pulley

It sounds to me that your belt or tensioner is worn, if the noise goes away when the ac is off then it is just the belt slipping, it takes a lot of power to run the compressor and if the belt is worn it most likely slipping on the pully when you engage the clutch.

start from bottom crankshaft pulley and ac compressor turn belt tensioner counterclockwise or lift forward then run pulley belt around crankshaft pulley and around AC compressor,run pulley belt around power steering pump then around alternator,once drive belt around alternator you done make sure drive is center of crankshaft pulley and AC compressor pulley.and belt back is center against water pump pulley before releasing the belt tensioner.

is your car at an idle when the a/c is engaged it takes power to run this circuit your engine will slow down. most cars have a sensor that will increase you idle when a/c is engaged. this also compensates for the added drain on the alternator

Too slow ??
The compressor is driven by the ac clutch which is driven by the serpentine belt, right ?
How do you know the compressor is running too slow ??

Bad compressor this work also when heater is on. To check have someone turn on ac/heater make sure clutch on air comp is turning. If not comp clutch is frozen

Open the hood and start the car with the a/c off. Do all the components running on the drive belt seem to be working ok?
Turn on the a/c and check to see if the symptoms repeat themselves...
If with the a/c off everything is ok, then you're probably fine to drive until you can get the a/c unit serviced.
If the symptoms are happening with the ac off, then it could be an idler pulley or a water pump or alternator, or powersteering.
Best bet is to open the hood and do a bit of inspection/investigation with motor running.

Sqealing belt is loose belt. Battery light on could mean loose or failing aternator for same reason. If belt isn't loose, use belt dressing. If this is helpful, please rate as such. TY