We have three York centrifugal chillers with the following spec
Series YT Codepak
Unit Model YTH3J3E35COG
Capacity 500 Tons
Compressor Model YDTL.126
Starter SSS 26L-50A (LCSSS)
One of them was under maintenance and we replaced its shaft seal. Now when it was taken again in service it has started tripping on 'half phase' fault.
I've changed the trigger board with a new one and also swapped it with the chiller which is working fine but to no avail.
Took the resistance readings of each thyristor as well as the J6 to J11 points on the cards. Found one thyristor short and replaced it. Now all the resistances of the thyristors are between 15 and 20 ohms as per the York Manual. Secondly, each of the points on the board has a resistance of around 200 ohm as per the board.
What could be the issue here?
The chillers have been service since 1996 and before maintenance it wasn't any half phase fault.