Can AC voltage phase change across an SSR?
Your voltage measurements just confirm that the SSR is not turning on.







simulate this circuit &ndash; Schematic created using CircuitLab

Figure 1. With SW1 open VM1 will read full line voltage and VM2 will read zero.

The PCS15-D-240A-25ZL has built-in status LED. This should turn on when you have > 4 V DC on the input. If the LED isn't on then check the input voltage and make sure that it is DC. Note that the LED confirms control voltage and not the output voltage.

If you can't get it going then add a schematic to your question and, perhaps, a photo of your setup.


  So is the SSR changing the phase of the power somehow ...?


No. It's just not turning on. I've written a little more on SSRs in Opto-triacs, solid-state relays (SSR), zero-cross and how they work