I recently purchased a used IEC Centra centrifuge with a refrigeration feature. Works great, except the refrigeration condenser never cycles off and as a result the chamber gets down to the minimum reading of -10C no matter what I set the target to. I've deduced through testing that the thermocouple works fine and it still manages to get extremely cold (I actually had a sample almost freeze) so I'm assuming the actual refrigerator coil is sufficiently charged and all.
I pulled the temperature controller board tonight and figured that it was probably an issue with the relay to control the condenser. Datasheet for the relay is here. I wired a lightbulb to the AC output and noted that as soon as line voltage was applied the lightbulb came on even though I had not connected anything to the DC side of the SSR. Am I correct in assuming that this means the relay is shorted and I should begin by replacing it? I have never verified if an SSR is working before.
Thanks
Best Answer
Yes, that would seem to be a correct deduction- SSRs will often fail "on".
You can also double-check by seeing if the drive voltage turns on and off with the temperature setting. There's a small chance that the failure is not confined to the SSR.