Which is the low pressure port for charging freon r12,lexus es250.

Depends on the year. Cars in the early 90's used R12. Anything later uses R134a. The size of the charge ports will define the R134a port. An adapter is needed to fit on the charging hose. R12 requires no such adapter. Ther charging label under the hood will tell you what refrigerant is needed too. Since you failed to give enough information on what make and model car you have, a general answer for the location of the low pressure port will be given. On the compressor, the larger diameter hose connection is the low side. Connect there, or look for the drier/accumulator (Large diameter silver container near the firewall). Connect there. You will need to access the AC information label under the hood to determine how much freon to add to the system.

yes, L is for low pressure side or suction, attach refrig. to this port

it is at the firewall....

R12.... In 1994 R134a was required, but some changed earlier. Yours may have been converted. If the service ports are threaded it still has R12. Hope this helps.

You want to use the R-134. But you have to locate the low pressure port in order to charge it. I am not aware of its position exactly due to variations between models and years but if you follow the lines off of the compressor you should eventually run into a low pressure service port. However you do have the correct freon for the vehicle.

Hi, determine if your car uses R134 or R12 refrigerant. You will notice screw type connectors on the both the High Pressure Side and Low Pressure Side lines in models using R12 refrigerant. R134 compatible models have quick connect valves on both sides. Models made before 1995 may use the old R12 refrigerant. If this is the case, you must have your Chrysler's air conditioning system retrofitted to use R134 refrigerant. Mixing R12 and R134 refrigerants is dangerous and may cause damage to your vehicle. Check your air conditioning system pressure using an automotive air conditioning pressure gauge. Keep in mind that in order to get an accurate reading, the air conditioner has be turned on the coldest setting with maximum blowing power. Remove the Low Pressure Side port valve cap and set it aside. The location of the port varies, but it is usually in front of the engine block. Attach the refill hose to the port on the Low Pressure Side of the air conditioning system. The Low Pressure Side port is smaller the High Pressure Side port. Because the ports are different sizes, the refill kit hose should fit only on the Low Pressure Side port. Additionally, the High Pressure Side port will usually have a red cap or be marked with an H or the word High Allow the air conditioner to **** the refrigerant out of the can by slowly turning the valve on the refill kit hose. Pay attention to the way you hold the can. Most kits will have you hold the can upright when you recharge the air conditioning system. It may take as long as 10 minutes to empty a single can. Turn the valve to the off position and remove the refill hose from the port. Recap the port before closing the hood. Let the air conditioner stay on for at least 30 minutes. This allows the refrigerant to move throughout the entire system.
Take care

First off it contains no R12 Freon. It contains R134a refrigerant. The low pressure port is located on the larger of the 2 aluminum pipes. The cap may be green, blue, or black. It should have an L on the top.

This hjas a possible two part problem, the first part is the a/c compressor has a clutch on the end of the shaft and is engaged with the a/c compressor switch turned on, which means while the car is running, you turn on the a/c and walla, you get cold air(as long as it is fully charged), the belt drives this clutch which in turn spins the inside of the compressor and starts to mechanically **** freon into it through means of the low(suction) side, the larger diameter port, once low pressure freon either 134a for everything built after 1994 or freon r12 for cars built before 1994 enters the compressor it is then compressed into a high pressure liquid which has a high pressure test port that is always smaller in diameter then the low side (fill) port.
When the clutch is engaged, it will only slightly rattle after it gets a few thousand miles on it however as the vehicle gets more useage and the a/c gets more useage(considered extreme condition useage) more use then normal vehicles would otherwise get, the clutch starts to wear out causing this rattle. A clutch head puller is used to remove the clutch can't do it without the proper tools, the belt must come off before doing the replacement.
Any parts store will have the tools and the clutch, you don't have to release any freon for this repair.
Another reason for a rattle could be the a/c system is low on freon and oil.
Buy a freon charge kit with a one pound can of 134a freon + oil combo and with the car running and a/c on high blow full cold attach the charge hose and freon into the low side port, rattle should cease soon as the vehicle reaches is full charge, should't take more then 2 pounds(cans) of freon, system hold 2 3/4 pounds empty each can is one pound.
Happy Motoring!!

R-12 if it has not been converted to R-134.....should be able to tell by valve on low side pressure fill tube...R-12 is getting hard to find....

Sounds like the A/C system just needs to be recharged. When was the last time you had this done? Just take it in to your mechanic and he can do it for you and if that's not it for some reason, then he will be able to find the problem but most likely you need more freon added.

Benjamin