I wish I knew. I have asked the same question!
You buy a can of R-134a refrigerant that has a guage. A/C Pro is a good brand but a little pricey about $44.00 Start your car and turn your ac on full blast to the coldest position and make sure the clutch on the compressor is spinning. It is very easy to tell, you can both hear it click and see it spin by looking at the front of the AC pulley. If the whole pulley is spinning then its on, if the front inside is stationary and just the outer ring is spinning then the clutch is not engaged and you will need to have it fixed. Assuming the clutch is working and your AC is on full blast, locate the shrader valve on the low pressure side. This is located right above the EVAP Solenoid thats attached to the firewall on the passenger side engine compartment. Connect your can and check the pressure. If its not in the green then squeeze the trigger on the can and continue to check periodically until it is in the center of the green. By that time your air should be coming out cold if everything is working properly.
Actually the first answer is not completely correct. even if the compressor pulley isn't running does not mean the compresor is bad. If there is a low refrigerant charge, the same symptom will occur.
A recharge kit from AutoZone or NAPA Auto Parts will cost between $9 and $20.Make sure to get one with a gauge. The port you want to access is the smaller of the two ports. The low pressure port is the one you want. It should have a blue or green cap on it.
Read the instructions on the can of refrigerant and add it to the system. Rad the gauge and make sure the pressure is in the correct area on the gauge. The proper pressure is indicated in a blue area on the gauge. If the compressor runs continuously after adding the "freon" then it should be getting cold in the car. As the temperature reaches it's thermo point , the compressor will turn on and off as cooling is needed.
freon usually goes on your condinser there should be a place to add collant on your condinser which is a silver cylinder
On the suction side, the low side...................
It is either on or near the recievr dryer in the right rear of the engine compartment. To corrrectly add freon, you need gauges and a refrigerant recovery system
R134a
Answering "Where do you add freon to your air conditioner in your ford ranger?"
There is one valve that is used to add refrigrant. But you had better not add Freon. Freon is R12 and your vehicle's A/C system does not have Freon (R12) as a refrigrant. More than likely it uses R134a.
Add fluid at the same place you check the level. You will need a long neck funnel.
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