Detari_SR

Hello everyone,

2000 ML430
93k miles

I'm having an AC problem similar to some others I have read on the forum. When the AC is turned on, it does blow air, but the air is NOT cold.
There are no clicking noises and the engine RPM does not increase when the AC is turned on.
With some research on the forums, I learned about the #44 30A Fuse and the low level of R134.
I found the fuse to be blown and the R134a lever to be LOW.
Replaced the blown #44 Fuse and added some R134 to the proper level, but the problem is still the same.

If any of you has any ideas that could help, i would really appreciate it.

Thanks in advance

P.S. The AC does not get much usage since it is cold most of the year, but last summer was working fine.

benz-tech

when your a/c compressor is turning- with the engine running. check the
8mm bolt in the very center of the front of the pulley. if it is not spinning with the pulley, your compressor has locked up. blown fuse 44's seem to eventually lead to compressor failure. they don't seem to like the 300+ psi that comes w/ no aux fan running.

MLW350

My a/c would not blow cold air with first use this year. Dealership charged $300 for a faulty switch. Compressor would not come on. There was enoough Freon and compressor works fine. It was only the relay.

I am not very mechanically inclined. Maybe someone else can describe what happen in better terms.

Benz_nut

I thought there was something wrong with mine too...turns out there was no freon left in my AC...you can buy a recharge kit at any autostore (autozone, murrays, pepboys), plug it into the lower line, and charge it...

Look for AC recharge kits in stores....

Darkmann

I hesitated responding becasue I have a 05 and the climate control system is quite different fom yours - at least the way it works. In any case, I had a similar prolem with my 05. In my case, the insides would fog up terribly on rainy days, there was barely any warm air and the cold air wasn't there at all. It was diagnosed to a faulty temperature sensor. That would require taking out the dash and I wasn't too happy. The looked further and found out that the control unit (I have no idea which one) that sends data to the temp sensor was the culprit. It was replaced and I have been having good air since March, I believe. Just my contribution.

benzeboy

If you have to add freon, there is a leak somewhere you need to get it fix to avoid costly repairs in the future.

ebrodnick11

My a/c isn't getting cold either. I checked that 8mm bolt and saw it wasn't turning at all. So I opened up the fuse box and replaced fuse 44 but still not getting cold or the bolt turning. Any help would be appreciated.

drmedro

I have a 2000 ml320 and last week on vacation i hooked up my new battery wrong, i know stupid mistake and also very expensive. I have changed fuse box, and abs computer. Everything works fine, drives good, great suv. Can anyone please tell me why my A/C is not turning on. The A/C problem is the only thing that i have not yet been able to fix.

Before the problem happen the A/C was blowing out very cold air!

I have changed relays, fuses, everything i am capable of doing, is there something i may have damaged?

Nexsen

I am sure you probably already know that adding too much freon can ruin the compressor. I mistook a problem for low freon and added some to an 85 MBZ wagon we had about 20 years ago and it caused the compressor to seize up. An expensive mistake and I should have known better. It is definitely better to use gauges to determine if the system is low before adding in. Some who do AC service have a dedicated machine that vacuums all freon out of the system and then they put back the right amount so there is less chance of a tech misunderstanding the gauges.

ESIII

Hello Everyone my 1999 ML430 is blowing air but not cold, my temp control knob would be cold at the red side and warm at the blue side (in other word there is something wrong) when it was working, now only warm air

ESIII

My ML 430 run really bad when it first starts up in the day, it crawls along for a while and it take some time before I can enter traffic. If I were to punch it, it take awhile to catch on...any thoughts

Maj. Dundee

The first thing that must be determined is when you press the A/C button the clutch on the compressor engages, meaning itshould turn along with the pulley.

If it doesn't then you are probably low on refrigerant. If it does, then wait a couple of minutes and go to the fire wall and touch both aluminum pipes, one should be cold and the other hot.

ESIII

I think the control knob is messed up because cold is hot and hot was cold, now it seems like like the switch moves too freely

vmystikilv

This is going to sound crazy but i had a ml430 and this is how i would solve it. Start the truck with the a/c system on. Open the hood and then let it drop and close. The shock would always kick in the clutch, and it would work for about a month and then I would have to do it again.

Maj. Dundee

'
That might very well be the case, but was it too much trouble to see if the compressor clutch was working and feel to pipes on the firewall?

sLickfITY

I am currently having a problem with my ac. When i press the A/C Button the compressor engages for a minute then it shuts off (pulley stops spinning). is it possible that it may be low on refrigerant? I could not tell if the pipes were hot or cold, or it wasn't noticeable. when i press the button again off then on it does not engage again unless i completely shut the car off and on to try it again. I also noticed the fans in front were not spinning. any ideas???

Maj. Dundee

Yes you are probably low on refrigerant. The fans won't run unless the compressor is running.

vinnienle

Please help... I had almost everything replaced for the A/C on my 2001 ML320: Air Door Actuator, A/C Expansion Valve O Rings, A/C Receiver Drier & O Rings, A/C Compressor & A/C Line (Comp to Cond). The A/C was working well for several months until today after I had a guy replaced the Power Steering Pump. The A/C is blowing warm air when turn on cold (the hot air is working fine). The A/C is on but the A/C Compressor is not turning on. Could this be a coincident that the A/C went out ... again? Or could the guy touch something while working on the Power Steering Pump?

Maj. Dundee

The only thing the P/S pump and the A/C compressor have in common is the serpentine belt.

The compressor does not operate off of a fuse or relay, but is turned on by the AAM (All Activities Module). But the AAM has nothing to do with the operation of the P/S pump.

So what you will have to do is remove both covers to the fuse/relay box. Then remove one or two additional screws and pull up the entire fuse/relay module out of the box follow steps 3-5. There is no need to disconnect the battery. Simply lay the module up side down onto a folded towel.

Then locate the X22 connector. In wire slot #9 you will find a PINK wire on one end of the connector and a BROWN/VIOLET wire on the other side.

Press the A/C button and then check both the PINK and BROWN/VIOLET wires for 12v.

vinnienle

Thank Maj. Dundee for your thorough instructions. I followed your instructions and found both wire to be 12v.

Maj. Dundee

Have you read post #12?

vinnienle

Thanks again Maj. Dundee. I read your post #12 and performed the check of the clutch on the compressor. It was not engaging and it was not turning along with the pulley. I'll will get refrigerant and report back.

vinnienle

Update...The refrigerant test was good so a friend and I spent an hour or so tracking down the electrical. He found the electrical connector at the compressor was loose so he pulled it out, cleaned it up and securely plugged it back. We ran a full test of the system again and everything seemed to be in good working condition now. We weren't sure but the guy did the power steering pump might have inadvertently pulled on it.

Thanks again Maj. Dundee for your help.

oria3

I situation no heat in cabin . when I turn switch to hot position ,air blowing any way cold. it happen reasently.

Papillon

My 2003 ml 350 135k stopped blowing cold air . The previous day I took the car to repair shop to replace power steering fluid pump and reservoir as it was leaking pretty bad . The mechanic also replaced the radiator same day as the hose to back fill tank ..the connection broke .. Anyway right after I got my car back realized ac is no longer blowing cold air ..took it back they diagnosed some relay went dead .. And explained that was stopping the fan to work .. The system was low on freon too but no leak so they also recharged it. Question to the forum any idea which fan they were referring to and did they actually forget to power connect the fan while replacing radiator or ps pump or the relay actually went bad and it's just a coincidence ?