Problems with the electric part

I really need help, the truck has no strength, stops when I turn on the air conditioning and does not make the changes well, the injection pump was already checked and has nothing and the box does not have mechanical problems either.
The mechanics to which I went told me that it is not a mechanical part but something on the computer or something of the electronic part.

It is a Nissan Serena 1997 Motor CD20 to Electronic Injection Turbo Diesel

You review all diesel filters if I am not mistaken you also bring a filter within the fuel tank.- Greetings Alfredo

I am aware of an alpha 145 that depending on the electrical demand is covered, whether to turn the steering wheel, put air, turn on lights or combination of them, and it is due to an unstable relief due to a failure in the body of butterflies that gives place to rely falling, that combination also does so due to the damaged or dirty flow

Before giving blind or deliberating sticks about the sex of angels. The diagnosis terminal would have to be put and make a check -up check.
The second thing would be to check the positive and mass feeds of the UCE, because taking into account that the pump is checked and the engine stops when a consumable (air conditioning) is placed, it should be verified that there is no tension drop in these feeds.

All the best.