I have a USA Spec 2002 ML320 with 140k miles. I am the original owner.

The car has not been driven much due to COVID and recently the A/C stops blowing cold air. Also noticed that the windshield does not defrost when getting fogged due to rain, etc. Maybe related, maybe not, so not sure.
The reason why I need a scanner is because the truck makes a few noises when the AC is turned on.

I checked fuse 40 - it is OK
I see that the compressor is spinning when the AC is on and when the AC is off. Someone said that on the 02's, the compressor is always spinning. but someone pointed out to see if the center screw is spinning. I have to check this.
Touched the low pressure hose and it is not freezing cold. It is cool, but not cold.

When I turn on the AC, I hear a noise from the center dash that is sounding like a whistle but not as high pitched, but only lasts for about 3 or 4 seconds.

My blower fan makes noise (w or w/o the AC on.) I may just have to replace it or clean it, but the sound comes from the air vent, not from where the motor is which i think is below the glove compartment. So i don't think it is the blower fan, but will take a look anyway.

Now this is the scary part that is making me want to get a scanner. Sometimes when I on the A/C, the car makes this noise like it is low on coolant and it sounds like you are dragging something. The coolant is at good level in the reservoir, and temp gauge is normal 80 degrees C. I replaced the water pump and thermostat at 120k miles just as part of routine maintenance.

Perhaps a bad aux coolant pump - will need to look into this - so need to read codes

So some questions.
Which is a good scanner that can read A/C codes? Which scanner can tell me what the pressures should be. I can also get a manifold gauge and connect to high/low to see as well.
What should be the pressures in the lines for the ML when it works normally?
Can anyone comment on the compressor running/turning all the time even when the AC is off? I
Any comments on the fan noise even when the AC is off.
I dont think i have a blend motor problem, but I could so not sure.

Thanks in advance.

 

My blower fan makes noise (w or w/o the AC on.) I may just have to replace it or clean it, but the sound comes from the air vent, not from where the motor is which i think is below the glove compartment. So i don't think it is the blower fan, but will take a look anyway.

Now this is the scary part that is making me want to get a scanner. Sometimes when I on the A/C, the car makes this noise like it is low on coolant and it sounds like you are dragging something. The coolant is at good level in the reservoir, and temp gauge is normal 80 degrees C. I replaced the water pump and thermostat at 120k miles just as part of routine maintenance.

Perhaps a bad aux coolant pump - will need to look into this - so need to read codes

So some questions.
Which is a good scanner that can read A/C codes? Which scanner can tell me what the pressures should be. I can also get a manifold gauge and connect to high/low to see as well.
What should be the pressures in the lines for the ML when it works normally?
Can anyone comment on the compressor running/turning all the time even when the AC is off? I
Any comments on the fan noise even when the AC is off.
I dont think i have a blend motor problem, but I could so not sure.

Thanks in advance.[/QUOTE]

Fuse 40 in the Eng. Fuse Box is for the sound system.

The A/C Compressor Clutch is supposed to spin whether the AC is on or off.

What center screw is spinning?

The low pressure is cool because you are low on Freon.

You should replace the Cabin Air Filter and remove debris from the blower motor.

If the coolant is at its correct level, then it is an A/C problem.

Are you referring to the A/C fans at the radiator?

 

Major Dundee - I knew you would come through - thank you sir. I've read your previous posts and responses on the subject.

I've changed the cabin air filter at 60k miles, i guess it is overdue.
The fan noise I'm referring to is the HVAC fan noise, not the radiator for or the A/C twin fan (which has not come on lately).

I just checked, the center screw of the compressor also turns even when the AC is off. So everything in front of the compressor turns with the serpentine belt. This is what I meant by center screw.

Also checked the coolant in the reservoir - , it is below the line when cold so am going to fill it.

Thanks for the icarsoft recommendations. I was looking at foxwell, Autel and Launch to see if they provide A/C pressures.

Do you know where the high pressure connector is for the A/C manifold gauge? I know where the low pressure is, and was going to fill it with R134a after checking pressure and figuring out how much i should fill. But I don't know where the high pressure connector is.

Thanks.