Polar 92ED Clamp problem

Hi Friends
I have a hydraulic clamp problem on a Polar 92ED. With the foot pedal clamp works /operates normally. When the clamping pressure is set at minimum when a cut cycle is done, the clamp comes down, knife comes down and goes to TDC and stops. Then clamp returns back to top. When I set clamping pressure 1200 on the big knob and a cut cycle is made clamp comes down, knife comes down and goes to TDC. The clamp remain at the bottom and very very slowly goes up. It takes about 4-5 minutes to reach the top.
Also I push the clamp up with a wooden block and clamp goes up with resistance. Y315 is on. Y27 and 27a is off. When the clamp reaches top the Y315 is off. Also the manometer shows zero pressure.
Can anybody you please help with trouble shooting this problem. Your immediate help is highly appreciated.
Please reply to dsgraphic@bellnet.ca