What do H and L mean?
H and L are markings used to distinguish between the high-pressure and low-pressure sides of the car's air conditioning system. H stands for high-pressure, and L stands for low-pressure.
Should you add refrigerant at L or H?
Adding refrigerant to a car's air conditioning system can be done in two ways, either at the high-pressure (H) side or the low-pressure (L) side. Adding refrigerant at the high-pressure side is suitable when the air conditioning system has been checked for leaks, evacuated, and is ready for use. When adding refrigerant at the high-pressure side, you should not engage the compressor during the operation, and the engine should be off. Adding refrigerant at the low-pressure side is typically used for topping up refrigerant. This method adds gaseous refrigerant, and the process is slower.
Steps for adding refrigerant:
High Pressure Side (H):
1：After evacuating the air conditioning system, close the high-pressure and low-pressure manual valves on the manifold pressure gauge.
2：Connect the hose in the middle to the refrigerant canister's injection valve, unscrew the nut on the manifold pressure gauge hose and the refrigerant canister's open valve. Wait a few minutes for the gas to escape before tightening the nut.
3：Open the high-pressure side manual valve, invert the refrigerant canister, and begin injecting refrigerant.
4：After injecting a certain amount of liquid refrigerant, close the refrigerant injection valve and the high-pressure manual valve on the manifold pressure gauge. Then, remove the gauge. Note that you should add refrigerant when the engine is not running to avoid hydraulic shock.
Low Pressure Side (L):
1：Connect the manifold pressure gauge and the refrigerant canister to the compressor.
2：Open the refrigerant canister's injection valve, loosen the nut in the middle of the hose near the pressure gauge, listen for refrigerant flow, and then tighten the nut to release any trapped air.
3：Open the low-pressure manual valve when the system pressure reaches 0.4 MPa.
4：Start the car, turn on the air conditioning, and then open the manual valve on the manifold pressure gauge to continue adding refrigerant until you reach the specified amount.
Please note that these steps should be followed with caution, and it's essential to follow manufacturer guidelines and safety procedures for working on air conditioning systems.
