Circuit board control is still good or defective?

My residence air condition is low gas pressure and it does not work. When I turn off main power (240v) to the compressor and connect the jumper from Y (out) in the circuit board control to the relay of fan and compressor, I notice that the relay work( that means 24v from thermostat goes through circuit board to the... show more My residence air condition is low gas pressure and it does not work. When I turn off main power (240v) to the compressor and connect the jumper from Y (out) in the circuit board control to the relay of fan and compressor, I notice that the relay work( that means 24v from thermostat goes through circuit board to the relay). But when I turn on main power, the compressor and fan begin to start, and just a second, the relay turns off, compressor and fan stop running. Do you think the compressor or fan has a problem? Then I bypass the circuit board control by jumper from Y(in) (or hot wire from thermostat) to the delay, compressor and fan start running. Please help me by let me know what the problem is, circuit board control or something else? Thanks for your advice.
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