Pressure transducer problem

[marc5180]

I was working on a Lennox unit KVHK48D the other day that has 2 circuits each circuit has 1 compressor, 1 accumulator , 1 condensor fan etc.

My problem is circuit 2 was tripping on HP due to high head pressure caused by an actuator that controlls dampers (which were closed) for the head pressure but each circuit doesnt have a seperate actuator/damper they share 1 on the condensor coil.

Also the pressure transducer that controlls the actuator is in the discharge line of circuit 1 only.
When circuit 2 starts up alone then the dampers are closed causing the HP to rise, it's only when circuit 1 starts up that the dampers begin to open.

For the life of me i can't figure out how it is supposed to work.

Why only have 1 pressure transducer controlling 2 circuits?

[Brian_UK]

Perhaps circuit 1 is the duty circuit and and second one kicks in when the load increases.

[marc5180]

That could be the case but the 2nd one starts up before the first one sometimes.

I tried ringing technical to ask them but i was put through to a guy in France that didn't know.