GM-45268-121 is used to replace the TXV when doing an A/C system flush with the ACR2000. To allow the R134A to flow through the A/C system, the metering device(TXV) must be removed. The GM-45268-121 is an adapter that is installed in place of the TXV and allow a flow through of the R134A. GM-45268-121 is used with the GM-45268 A/C flushing kit.