The air conditioning system on a 1998 Ford Explorer uses pressurized refrigerant gas to cool a series of pipes which then have air run over them. This air is drastically cooled and then blown into the Explorer's cabin to cool it. When the pressure of the A/C system is no longer high enough it will not be able to cool the pipes properly, and the air being blown in will not be cold. In order to fix this problem you will need to recharge the A/C system using refrigerant to increase the PSI in the system, restoring it to its intended pressure and enabling it to cool properly.
Remove the cap on the low pressure port of the air conditioning system and hook up the low pressure gauge (the blue one) to the A/C system.
Remove the cap on the high pressure port of the air conditioning system and hook up the high pressure gauge (the red one) to the A/C system.
Hook up a canister of R134 refrigerant to the other hose on the A/C gauge.
Allow the R134 to charge the system until the low side is between 50 to 70 psi.
Disconnect all of the gauge hoses and replace the caps on the ports.
