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Electric jacks: motors, current and manual retract

An electric leveling jack is a motor and gearbox on a screw leg. The controller can't see the jack, only its Hall signal and its current, so most electric faults are a broken signal path, a bound jack, or low voltage.

The short version

What's inside a Lippert electric jack

Each Ground Control landing gear leg and jack has its own Hall effect motor, which Lippert sells on its own as part 343758. The motor and its gearbox drive the leg, and the harness carries motor power plus the Hall sensor circuit back to the controller.

The controller works from two signals. The Hall signal tells it the motor is turning, which is how it follows travel. Current tells it the jack hit something: ground on the way down, the stop on the way up, or a bind. So 'Unexpected high amp stall' is a current problem, 'Out of stroke' is a travel problem, and a special jack error is the Hall or motor circuit.

Twist prevention isn't a fault. If single rear jacks won't move in manual but work fine in auto, the controller has locked them out to protect the frame.

Homing: why the controller forgets a jack

After a special jack error, a motor or jack replacement, a manual override or a controller swap, the controller can't trust where that jack is. Homing runs every jack up to the hard current limit and uses that as the reference again.

  1. Fix what caused the error first: harness, connector or motor.
  2. Extend every jack so it has at least 6 in to retract: Front for the landing gear, Rear for the rear jacks, Left and Right together for middle jacks on a 6-point.
  3. Press and hold Retract until all the jacks start retracting. They stop at the hard current limit and the error clears.
  4. If they won't retract, Lippert says look for a wiring interruption. Rev. A controls need the same 6 in, then auto retract.

Proving the jack, the harness or the controller

A special jack error names one position. Your job is to decide whether it's the jack itself or the path from the controller to it, before anybody orders a $500 motor.

  1. Load test the battery. Ground Control wants 12 V or more under load and quits under 10.8 V.
  2. Run that jack alone in manual. Lippert says if auto misbehaves, test each jack with its own button.
  3. Check the harness at the controller and at the jack, look for chafe and rodent damage, and check the fuses at the controller.
  4. Look at the motor itself. A motor that has rotated on its mount can pull its connector apart, so check the mounting bolts too.
  5. If the motor runs but the leg doesn't move, it's mechanical. Pull the motor and run it by itself: if it turns its shaft, the leg's gears or screw are bad; if not, the motor or gearbox is.
  6. Fix it, home the jacks, and run a full cycle.

Power Gear electric jacks

On Power Gear's motorhome electric system the control runs the current test for you. It flags a motor drawing too much current (short), too little (open), or running too long out or in, then blinks Auto and Man with the corner lights for the jack. In error mode you can run one jack: hold its corner buttons with Auto to extend or Man to retract.

These jacks have a brake that holds the load when the motor stops, and the manual retract goes through it. That's the one place an electric jack can drop a coach on you.

Manual retract on electric jacks

Lippert Ground Control: unplug the motor power harness and pull the rubber plug on the motor. A top override takes a 3/8 in square drive straight in with no socket; a bottom override takes a 5/16 in socket. A 12 to 18 V cordless or a pneumatic screw gun is fine, but Lippert says no impact driver because it can damage the motor. Home the jacks before the next auto level, and on a fifth wheel pull the pin and raise the landing gear inner legs by hand.

Power Gear electric: ignition off, brake set, transmission in park or neutral, air bags reinflated if equipped. Put 12 V straight on the motor leads, and if the jack extends, swap them. Raise each jack until its pad clears the ground, then fully. If the motor won't run, pull the boot, press the release handle lock, turn the brake release handle about 10 degrees counterclockwise, and turn the override nut clockwise (viewed from below) with a 16 mm socket.

Careful: Releasing a Power Gear electric jack's brake lets a loaded jack retract suddenly and the coach can drop. Keep out from between the tire and wheel well and from under the bays while you do it.

Common electric failures

Most of these are found with a meter and a flashlight, not a parts order.

On the job

  1. Note which jack the error names and whether its motor makes noise.
  2. Load test the battery; Ground Control quits under 10.8 V.
  3. Run that jack alone in manual and watch it.
  4. Check the harness at both ends, the controller fuses, and the motor mount.
  5. Motor runs and leg doesn't move: mechanical. Motor silent: power, harness or motor.
  6. Override by hand if you need it up: motor unplugged, drill or ratchet, no impact.
  7. Home all jacks (6 in of retract each, hold Retract), then run a full auto level.

Numbers

Shop tip

Before you condemn a Ground Control motor, swap that jack's connections with its partner on the other side at the controller. If the fault moves sides, it's harness or controller. If it stays put, it's the jack.

Where this comes from