Probably due to slipping when they get wet. Your belts might need to be changed.
The AC belts are probably stretched and loose. I had the same problem and replaced belts and cured squeak.
Put a small dab of clear dialectic grease on both sides of the belts and the squeak will go away.
There are probaby many reasons but one that I know of is anti-freeze. If some anti-freeze gets on the belt it can cause a squeak and it's hard to get rid of it without replacing the belt.
It might be one of your belts. Check the inside of each belt (the part that contacts the pulleys) for shininess or cracking. If the belts are okay, then check and/or tighten the tension. Steven
A fan belt may squeak or slip badly in cold weather due to it being stiff from the weather. However, most likely you will need the belt replaced.
If there is any oil, power steering fluid, or antifreeze on your belts it may cause them to slip and squeak regardless of how new and how tight they are. If you have a fluid leak wetting the belts, this leak must be repaired. If the fluid contamination is from any type of oil (including PS fluid) the rubber of the belts may be damaged and the belts will have to be replaced after repairing the leak. Also, you want to be sure that it IS in fact the belts squeaking. Try running the engine with belts removed. It it squeaks without the belts in place, something else is causing the squeak. Also, with the belts removed and the engine stopped, try spinning each pulley (that the belts normally spin) and note any that make noise, feel wobbly, or have a rough (not smooth) feel to the movement.
no Yes, it can cause the belt to squeak and slip.
Probably one of the fan belts is loose or glazed from slipping. Before you start it next time take a bar of handsoap and lightly rub it across the underside of the belts. If the squeking stops you need to have your belts checked and/or replaced.
This is almost always caused by worn drive belts. Replace all the belts at the same time. If it has a serpentine belt, then replace it. Be sure and check the idler pulley to make sure the squeak is not coming from the idler pulley itself. Another possibility is a bad alternator, water pump, or power steering pump. Check them all.
A belt that is loose or glazed over can cause a squeaking sound. Make sure the belts are tight and in good repair. If they are you can try some belt dressing, they sell it at auto parts stores.
I would first look at the fan belt or belts. This is the most common cause but you could have other problems including worn idler pulleys.
brakes or belts check those first. a bad belt can fool ya