Can you safely change a four-prong electric dryer outlet to a three-prong 240V air conditioner outlet?
No. Call an electrician. 50 dollars is cheap compared to having your dwelling burn up.
If potential is constant throughout a given region of space can you say that electric field is zero in that region?
the belt tensioners are on the alternator and the air conditioner. On the alternator, you would have to loosen the 2 bolts that are on the tension bar. On the air conditioner, you would have to loosen the tension bolt and you would also have to loosen a bolt that is behind the air conditioner pulley. You would have to turn the pulley to get the holes to line up to the bolt to loosen.