How to Recharge Air Conditioner ML320 W163 1998-2005

Last updated: October 24, 2026

How to recharge the Air Conditioner (A/C) system of your ML-Class W163.

Applicable to ML320 ML350 ML430 ML500 ML55 AMG 1998-2005

Before we begin, remember that these instructions may vary depending on the AC recharge kit you are using. Be sure always to read the instruction notes on your recharging kit.

1. Turn the engine on and let it idle. Turn the air conditioner ON and set it to the maximum cold setting.
2. Open the hood of your ML320 W163 and locate the low-pressure AC service port, and remove the cap.
3. Attach the refrigerant gauge to the service port. You will need to press and hold the quick-release at the end of the hose, insert it into the AC charging port, then release it.
4. Read the pressure in your air conditioner system. If the pressure is low, the gauge reading will be in the white zone. If the pressure is normal, then the gauge should be in the green zone. You should not have a reading in the HIGH/RED zone except when the car is turned off, in which case it is normal.
5. Always keep the can UPRIGHT. As you charge the system, shake the can slightly every 2 or 3 seconds while charging.
6. Every 30 seconds, release the trigger to stop the charging process and read the pressure. Make sure it is not in the RED zone.
7. Stop recharging the system when the pressure gauge shows normal, in our case, it should be in the middle of the green zone.
8. Detach the connector from the low-pressure AC port. Reinstall the cap, close the hood, and enjoy your AC system again.

The green zone depends on the outside temperature

This is the part that catches most people. Pressure on the low side of an air conditioning system rises and falls with ambient temperature, so there is no single correct reading. A system that belongs near the bottom of the green band on a cool morning belongs higher up the band on a hot afternoon. Better kits print a temperature scale or a small chart on the gauge for exactly this reason, and the first kit listed below has one. Use it, and take the reading with the hood open and the engine idling, which is the condition those charts assume.

Getting this wrong goes one way, which is too much refrigerant. An overcharged system cools worse than a correctly charged one rather than better, and it works the compressor against high head pressure, which is how a cheap can turns into a compressor bill. If you have been adding refrigerant and the air at the vents is getting warmer instead of colder, stop. That is what an overcharge feels like, not a sign that it needs more.

If the system swallowed a whole can and still reads low, it has a leak. Refrigerant is not consumed by a working air conditioner and does not need topping off on a schedule the way engine oil does, so a system that went empty lost its charge somewhere. That is also the case where recharging is the wrong move: releasing R-134a into the air is what section 608 of the Clean Air Act prohibits, and a system you refill every summer is releasing it a can at a time. A can with dye in it, or a shop with a sniffer, will find the leak so it can be fixed once.

What is the best A/C recharging R134a kit to use?

It’s up to you to choose the recharging kit you prefer. There are many A/C recharging kits available, but as you make your selection, there are a few things that you should keep in mind. Things to look at when you make the selection are:

• Does the R134 refrigerant have any oil added?
• Does it have dye to help you find leaks if the system doesn’t hold pressure?
• Does it have any leak sealer?

	A/C PRO ACP-100 Professional Formula R-134a Ultra Synthetic Air Conditioning Refrigerant with Reusable Dispenser and Gauge, 20 oz This kit includes a gauge for adjusting the outside temperature. You can know the exact pressure range you need to be in.
	Interdynamics MAC-134 EZ Chill Refrigerant Refill with Charging Hose and Gauge, 18 oz A/C refrigerant has oil and leak sealer mixed in.

Important Notes

• Wear eye protection and gloves. Liquid refrigerant escaping a hose or a loose fitting is cold enough to cause a frostbite injury instantly, and there is pressure behind it. Connect a DIY can only to the low pressure port, which is the only one its hose and coupler are built for.
• Think carefully before using a can with leak sealer mixed in. Sealant is meant to plug a small leak, but it cures where it meets moisture, and that includes the inside of a shop recovery machine. Some shops will decline to service a system once sealant has been through it, and that refusal costs more than the leak would have.
• DO NOT TURN THE CAN UPSIDE DOWN WHILE CHARGING. Only gas should go into the AC system, by turning the can upside down the AC system will get liquid refrigerant which can cause the AC compressor to lock up and also wash out the oil. Keep the AC refrigerant can in the up position and only shake it slightly while charging.
• If the refrigerant level is very low, the AC compressor will not engage. Charge the AC system for a couple of minutes with the engine running, and you should notice the AC compressor engage once you add enough refrigerant to the system.
• If your gauge is not working correctly, it’s probably because your compressor is not spinning. The AC compressor stops spinning when it’s low on refrigerant. Add some refrigerant until the AC compressor kicks in, to get a pressure reading.

Where is the A/C charging port located?

The A/C charging port on your ML W163 is located on the passenger side of the firewall. Look near the battery and the coolant expansion tank. You will see the A/C line and the black plastic cap on top of the A/C low-pressure line port.