How to Charge the Air Conditioner on a '99 Ford Expeditionby Ryan Bauer; Updated November 07, 2017
Low refrigerant levels can cause your Expedition's air conditioner to output air that is much warmer than your target temperature. Thankfully, you can restore full performance by recharging the refrigerant to factory pressure levels. Consumer recharge kits will include everything that is needed in a single unit, including a pressure gauge, hose and the canister containing the actual refrigerant.
Raise and support the hood. With the engine turned off, locate the metal air conditioning line, which runs sideways along the very back of the Expedition's engine bay. There is a service port on top of the tube covered by a black plastic cap. Remove this cap.
Screw the hose of a R-134a recharge system onto the service port. Start the engine and turn the air conditioning to its highest setting. Return to the engine bay to check the pressure gauge on the recharge system. If the gauge indicates the pressure is beneath the green-colored area, the coolant levels are too low and the system will benefit from a recharge.
Hold down the trigger on the recharge system for several seconds at a time, then pause to check the gauge again. Continue this process until the needle is in at least the middle of the green section.
Turn off the engine, detach the hose and replace the cap on the service port. If the canister does not appear to be empty, you can save it for future use.
If a leak is suspected somewhere in the system, a recharge kit containing UV dye can be used to help pinpoint the location of the leak.
Keep appendages and clothing away from any moving parts of the engine.