Chart D4, Extended Pump Operation
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- Pump/motor assembly is designed to provide hydraulic accumulator with specified pressure. Pump/motor is controlled by pressure switch. Pressure switch closes, which activates pump/motor. This circuit grounds relay coil.
- Positive circuit for relay coil comes from 5-amp pump relay fuse. Power for relay comes from a 30-amp fuse, located in engine compartment. When pressure drops to 2030 psi (14,000 kPa), pressure switch circuit closes, grounding relay coil.
- This activates relay allowing pump/motor to operate. When pressure reaches 2610 psi (18,000 kPa), pressure switch circuit opens, deactivating pump/motor. "BRAKE" lamp circuit is powered by 20-amp fuse. Circuit is grounded if parking brake is applied, fluid level is low or pressure is low.
- When low hydraulic accumulator pressure is detected at the pressure switch on the hydraulic unit, the pressure switch closes to provide the pump motor relay a path to ground, causing pump to run.
- This chart checks pump during extended operation for pressure, leakage, fluid obstruction and pump failure.