High pitched squealing noise from the motor.

What is your question?

I heard a very high pitched squeal come from the motor one day when making a turn. I thought it was just the power steering unit making the noise so did not think much of it. We then had other incidents but it seemed more associated with the air conditioning. Took it in to our mechanic several times but he could not find the problem. Even had him drive it for 2-3 days but it never made the noise for him. It is hard to describe other than it is extremely loud and only lasts for a short time. It has gotten to the point where it only happens when the air conditioner is turned on but does not continue to make the noise over and over again. Will go for about 45 seconds. Assumed it was the air conditioning compressor?????? We just decided to drive it until it broke down but that limits our use of the van to local driving and no air-conditioning unless absolutely necessary. We did not want to get out on the highway away from home and have some major problem.