Porter, R.D. Aderhold, S. Alsberg, L.E. Cravatta, A.T. Drury, M.A. Gaitan, G. Gonnella, D. Holzbauer, J.P. McCaughan, M.D. Nelson, J. Neveu, N.R. Posen, S. Stilin, N.A. Wilson, C.M. Zacarias, L.M. JACoW Publishing Geneva, Switzerland 2673-5504 978-3-95450-234-9 10.18429/JACoW-SRF2023-MOPMB081 English 302-305 cryomodule cavity linac operation vacuum Contribution to a conference proceedings 2023 2023-09 https://doi.org/10.18429/JACoW-SRF2023-MOPMB081 https://jacow.org/srf2023/papers/mopmb081.pdf The LCLS-II project has installed a new superconducting linac at SLAC that consists of 35 1.3 GHz cryomodules and 2 3.9 GHz cryomodules. The linac will provide a 4 GeV electron beam for generating soft and hard X-ray pulses. Cavity detuning induced by microphonics was a significant design challenge for the LCLS-II cryomodules. Cryomodules were produced that were within the detuning specification (10 Hz for 1.3 GHz cryomodules) on test stands. Here we present first measurements of the microphonics in the installed LCLS-II superconducting linac. Overall, the microphonics in the linac are manageable with 94% of cavities coming within the detune specification. Only two cavities are gradient limited due to microphonics. We identify a leaking cool down valve as the source of microphonics limiting those two cavities.