'97 Explorer XL ,Loud Sound and Lurches When Heat or Air is On

[qweenofyou]

I hope I'm describing this well because it's a strange(to me) problem. When I turn on the air conditioner or heater, there is a loud noise and the vehicle "lurches" as though something is stuck or locking up. It happens if the fan is on by itself too, but not as fast, and not with the lurching. I just bought this truck so I don't have a lot of history. The first time it happened the air was on and cold and I was moving forward from a stop and the noise and lurching started, then stopped when I turned off the air. The previous owner advised the heat takes a long time to kick in and I was advised that I would have to turn on either from a full stop, not while driving or they wouldn't work at all, just blow air. As it is now I don't dare turn on the heater because it sounds like the vehicle is going to blow up so I don't know if it's heating or not. I'm hoping someone here can point me in the right direction. I don't have too much experience but can follow instructions in any manual if I know what to look for.