Where is the low valve located on my car

That's a good question. I can't find the low pressure service valve on my 2004 Taurus (similar car), and I've been doing A/C work for decades, I hate admit. So, with engine off, I infuse a can of 134a into the high side valve, then start engine and take a pressure reading off the high side. Awkward way of doing it, but it works. It works best on a cool engine and you can push the 134a into the line by gently warming the can with a hair drier. Warning: The can, can not withstand "high side" pressures that develop when engine is running. You are to switch over to gauges before starting engine. YouTube video may be able to help you. I'm too old to learn.