royis, one thing you should check if the pump motors does run when you are trying to extend the left rear jack is the vlave "T" on the pump manifold. Make sure they are all closed; turned clockwise. If not this could allow the fluid back into the resivoir. If this does not corrct the problem let us know with a little more detail as to what is going on.
Mike, RVIA & RVSA Certified Master RV Technician
Amy, Dr. Assistant - Roxie & Mei Ling, four legs each
2000 Gulf Stream Scenic Cruiser 450 hp & 1330# torque
06 Saturn Vue, 06 Chevy Z71 4x4 & 2014 Corvette Z51 M7