This vehicle uses R134A refrigerant and the connectors that it uses are not interchangeable or reversible(on the vehicle side). That doesn't mean you cannot screw it up, if you were to connect the hoses to the wrong side of your manifold set, but if you are using the auto parts store recharging line and little cans of R134A they will only connect to the low side port.
Coincidentally if you look up at the hood above where the low side port is you will see a sticker with the amount of regrigerant and oil that your particular vehicle uses. Mine has the rear AC so it uses 3.75 pounds of "freon."
The Villager does not have a test port, you need to tee into the line near the fuel filter to test pressure.
The Villager does not have a test port. You need to tee into the line at the fuel filter.
Under the dash to the right of the steering column.
Under the hood, right side, in low pressure line.
The OBDII diagnostic port is under the dash to the right of the steering column.
The Low Pressure Side port is located on the line coming from the the compressor. It can be identified by the black cap marked LOW.
Freon is added to the lower pressure line port. It is the only port a refill kit will fit. I suggest taking it to a shop that does A/C repair if you do not know that already.
Under the dash to the right of the steering column.
Through the low side A/C port.
directly below the steering wheel at the bottom of the dash
There is generally a test port on the injection rail.Make sure you use only a high pressure tester and proper test fittings.The pressure is quite high and can be a serious fire hazard if not done right.
Error codes on a 1997 Mercury Villager can be found by connecting an OBDII code reader to the diagnostic port. The service manual has a full list of error codes and their causes.