I call it the poor man’s voltage check. Raise the lift to full height with no weight. Raise it until the cylinder reaches full stroke at full height. Once the cylinder bottoms out, continue pressing the up button for about three seconds or so. At this time THE MOTOR SHOULD NOT STALL. The PRV (pressure relief valve) should engage then and start bypassing the fluid through the PRV outlet. Typically a screeching sound emits as the fluid passes over the PRV under pressure.
IF THE MOTOR STALLS, typically that is a sign that you do not have 220V power to the motor. When you suggest that the motor is staining, it suggests that the motor is indeed stalling due to lack of power. The motor should always continue running during PRV stage.
Typically, when a lift is giving evidence of lifting only half weight, it usually is indicative of the motor running at half voltage. Most older 220V power units will operate on 110 volts for a limited amount of time before permanent damage to the motor occurs.
Check and double check your line connections. It sounds like you dropped a leg.
If you are saying that the motor does continue to run, yet the pressure seems to be lower than the OEM factory setting which is resulting in lesser weight being lifted, like mentioned, the PRV may need to be adjusted higher. But do refer to the factory setting before making adjustments. If your lift is a chain-over (roller) style, pressure ranges for those types are typically in the 2400-2850 PSI range depending on the lift capacity.
