Can I use R134 Freon in my 89 Grand Marquis to recharge the air conditioner?

No. Your system refrigerant capacity is 3.25 lbs. of R-12, not R-134a. Don't waste your money trying to convert from R-12 to R-134a--the results are usually awful.

Low side gauge (evaporator suction) is 25 to 50 psi, at sea level and 80 degrees F.

High side gauge (discharge) is 160 to 250 psi, at sea level and 80 degrees F.

Reading this link should help:

https://www.askmehelpdesk.com/cars-t...ml#post1864159

Yes yes it can be converted very easy, the simple kits they sell at places like Pep Boys, or Auto Zone does it very easy, the only real trick is that you have to by pass the condenser to make it run with no pressure while you add the new 134.

Did mine for less than 50 dollars and took less than one hour, and that was with a broken leg and no help
** I have the same car, except it is a 91.