Hello all! Been having an ac issue. Yesterday when I started the suv and let the inside cool down, it was not blowing cold. I used the ac charger and the pressure after fill was about 40-45. Today I started the suv and ran the cold air. Did not turn cold and checked the pressure. It now reads 102psi. Does anyone have any idea of the issue?

 

Update: Decided to drive the ML and when I got home started the GL. Put the ac pro gauge back on and now it was at 35 psi and blowing cold air. Any ideas?

 

No direct experience with A/C issues but observing techs working on A/C problems the SOP is to connect the A/C machine to the car's A/C system and measure low and high pressures. And insert thermometer into center vent, turn A/C on max and close all vents but the center vent. Outlet temperature is dependent upon ambient temperature and the factory service manual probably has a chart that for a given ambient temperature the outlet temperature should be such and such and the low and high pressures should be within some range as well.

Not sure what it means if pressures are too high. More often the pressures are too low. If pressures are low this can be due to low refrigerant level which means a leak. Oh have to mention it is not uncommon for the valves (Schrader?) in the A/C high and low pressure connectors to be bad and the source of a leak. Some mechanics replace these valves just on general principle.

The system is evacuated and the amount of refrigerant removed noted. If less than called for there's a leak. The system is subjected to a vacuum which can turn up a "big" leak but a small leak maybe not. (The connector valves I mentioned above can be responsible for a small leak.)

The tech will inspect the system for any leak sign. If a leak suspected but not obvious the system can refilled with the proper amount of refrigerant and with some dye added. The A/C system is run -- the car could be handed back to the owner to drive for a day or so -- then brought back in the service bay and signs of a leak using a black light are looked for.

Other possible problems are also checked for. Things like radiator fan not running. Blower motor not running. Air control doors/flaps not working right. A/C clutch not engaging. (This can be due to incorrect pressures.)

And so on.

 

Update again. Started the suv to cool the interior and had it running for about 20-25 minutes and the ac is not cold. Check refrigerant with ac pro and pressure is at over 100psi. I checked the compressor and clutch is spinning.

 

There are AC troubleshooting charts all over the internet. There is nothing special about Mercedes's AC system. Except maybe it doesn't work all that well. The Germans don't like people to be too comfortable, or something.

You need a two gauge system, one on the high pressure side and one on the low. For a couple hundred bucks you can get a gauges system plus a vacuum pump, and you are set to go. There are plenty of available tables that show the high and low pressures you should be seeing.

Rockster gave you a bunch of information, and based on your following post, it looks like you either didn't read it or didn't understand it. I don't mean to be harsh, but you don't seem to know whether you are measuring the high or low pressure side. My guess is, if you don't know, or only have one gauge, you probably are on the low pressure side. You probably badly overfilled the system, and there is not enough pressure drop going from high to low, so the system basically can't run. Dump a bunch of that R-134 out until you get down to under 50 psi on the low side.

But really, if you want to be maintaining that AC system, you need a set of gauges and a vacuum pump. You only have half the information you need.

 

I am measuring the low side. The odd thing is, is that I drove it and then it started getting cold. Turned around to go home to put the gauge back on and when I did, the psi was at 40 and it was cold. I just don't get it.

 

Your compressor is likely on it's last tour.

A few things to do, just in case:

• Start the vehicle and let it idle for a couple of minutes to ensure the a/c circulates refrigerant internally.
• Evacuate any air from your a/c ystem by pressing the valve on the low side until a little refirgerant comes out (not just air). Do this in short bursts until you notice refrigerant coming out (wear appropriate safety gloves and goggles).
• When attaching the charger canister to the system, evacuate the charger air line as you attach it to ensure you are not adding air to the system (press the charger trigger 0.5 seconds as/before you attach it).
• Add refrigerant as needed per the can's instructions.
• Allow the refirgerant a couple of minutes to circulate through the system.
• Check the low side metal a/c hoses for temperature. They should be cold to the touch. If not, you likely need a new compressor.

Follow all appropriate safety precautions when working with your a/c system.

 

If the system is full and you are getting wacky numbers the high-pressure, switch/sensor might be bad.