Junior troubleshooting problem

A customer complains that their motor keeps turning off when it is lifting a load. 

 The motor is a 480V 3 phase induction run motor which powers a lift gate for a loading dock.  When a load greater than 500 pounds is placed on a metal plate, the plate activates a pressure switch that starts the motor and moves a lift gate which lifts the load up so it can be loaded onto a truck. There is an emergency stop button and flush mounted start button near the loading dock platform. There is a limit switch that stops the motor when it reaches the loading lock.

The motor is accessible under the loading dock.  It is fed from a combination starter located in sight (per NEC) of the dock.  The combination starter contains a fusible disconnect, magnetic motor starter, control transformer, and selector switch ( hand-off-auto).  When in HAND position, the motor runs when the start button at the dock is pressed and held and the pressure switch reads more than 500 pounds, no memory.  In the AUTO position, when a load 500 pounds or greater is placed on the plate, the motor starts automatically with memory and shuts off when the load reaches the limit switch.

The combination starter is fed from a 480V 30 A 3 phase breaker in a distribution panel located 150 feet away from the loading dock. All control devices are 120 volts fed from the combination starter.

Answer the following questions indicating what test equipment you would use, the setting, and how test leads are connected.  Give reasoning for your answers. It may help to draw a ladder diagram to assist you in determining the order of troubleshooting.

1.  What is the first thing you check upon arriving at this site?

2.  Determining that step 1 was not the problem, what do you check next?

3.  Determining that step 2 was not the issue, what do you check next?

4.  Finding that step 3, was not the problem, you decide to do a test. You go to the combination starter and place the selector switch in the HAND position. You place a load greater than 500 pounds on the plate. You press and hold the start button and the lift works fine.  You switch to the AUTO position; You hear the motor start and the plate starts to rise.  About 6 inches above the floor, the plate stops and you hear the motor is off.  Where do you go and what do you check ?

5.  What is the problem?