Thursty

So I replaced the A/C compressor on my wife's 05 C230. I seem to remember reading somewhere that if the system was empty it won't take any freon because of a low pressure switch. I'm taking the car to the shop today to have the system vacuumed and freon added, but I can't for the life of me find out if there is a low pressure switch that I need to have them bypass.

ot1

Do not worry about the shop bypassing the low pressure switch once they vacuum the system, which can take an hour, the vacuum pump is then isolated BUT if there are no leaks the vacuum will be maintained observed on the manifold gauges. Its important to vacuum all connecting hoses, if the procedure is done properly there will be 4 hoses involved, Vacuum pump hose, Charging hose (134a), Low pressure hose, High pressure hose. Once the vacuum is drawn to -29 Hg, and maintained for an hour, with the vacuum pump isolated, then the 134a will be sucked into the vacuum when the 134a tank valve is opened, and so the low pressure switch will be tripped and allow the compressor clutch to engage, to allow filling the system completely. However before vacuuming the system it should be filled with nitrogen and the pressure monitored for an hour, because you can have leaks that only show up with pressure and not show up with a vacuum because a vacuum can and draw seals tighter.

tjts1

Low pressure switch? AC clutch? An hour? What car are you talking about?

ot1

...

ot1

An 05 C230,06 E320, 06 S550, 05 Expedition, 97 E350, well I could spend a day listing vehicles.

tjts1

There is no low pressure switch or clutch on this system. Do your homework.

ot1

OK no clutch, but certainly a pressure transducer. But my point was that an A/C tech or the OP would not have to be concerned about jumping anything if a vacuum is pulled on the system first. And you debated an hour? Slow leaks can take a while to show up, and depending on the CFM of the vacuum pump can easily take an hour.