1997 Toyota Corolla when I turn my car to the left it becomes very hard

1997 Toyota Corolla mileage: 40,000. Sometimes when I turn my car to the left it becomes very hard to steer, like it has been turned too far but it hasn't. This is at slow speeds like in a parking lot. It becomes almost impossible to turn as if it has no power steering. Also, you can hear a hissing noise from the left side. Never happens when turning right. Seems to happen the more you turn it. I checked the fluid seems to be full.