Mahle Robinair inside the machine, be sure to replace any panels you've removed before you start the machine. A closed housing is needed to properly operate the venting system that the machine must have to meet the SAE standard (Figure 7). Figure 9: Locate cover for access to oxygen sensor on Robinair machine. Figure 7: When you remove external covers from an R-1234yf machine to perform service, as from this Mahle Service Solutions ACX1280 unit, be sure to securely refit them before starting up the machine so the internal ventilation system works as designed. Pre-Charge Gross Leak Test Robinair The recovery and recycle steps are the same as for R-134a machines, with recovery specified at 30 minutes maximum. But the evacuation procedure for air removal starts with a pre-charge leak test. The machine must pull down to at least 26.6 in/Hg for at least five minutes and hold that for at least 3 minutes. Then isolate the system and shut off the vacuum pump. If there is a vacuum decay of greater than 2 inches in 5 minutes, this cycle is aborted and the technician gets Figure 10: Disconnect oxygen sensor harness, then use flat-blade screwdriver to remove sensor. Robinair the choice of trying again or pressurizing the system with 15% of the specified charge and going through a leak detection check with an electronic leak detector that meets J2913 (your J2791 detector may also be certified to J2913, so check with the supplier). This is a gross leak test and is intended to avoid charge of an expensive refrigerant into a badly leaking system. Perhaps these additional steps add 12-15 minutes to the Figure 8: Replacing an inoperative oxygen sensor for the refrigerant identifier is indicated by either of these warning notices that appear on the display of the Bosch/Robinair AC1234-6 machine. October 2015 5 MACS Service Reports