head pressure

[pigman149]

working on a mitsubish pu-p5ygaa changed comp and pcb now head is 150 psi and suction is 0 psi. head pressure is controlled by the twin fans,but how are they controlled,as help desk keeps saying there is a blockage but i see no evidence of this.
any help would be grand
thanks Ian

[Yuri B.]

The suction valve is not left closed by chance?

[pigman149]

no every thing is open. what did happen when i was there is,on first turn on the above happened and i remember the fans were running flat out,i then turned it off at the indoor units.switch on again and the head pressure went up to over 300 psi and suc to 90 psi and the fans were running very slow,then i turned off at isolator as pressure was getting to high,turned on again and now just getting head 150 suc 0 fans running flat out.could this be a fault with the sensors that control the fan speeds and not a blockage ?