C.P.

Hello,

I have a 2000 ML320. The a/c has become intermittent. When the outside temperature is cooler, the a/c works fine. When the outside temperature starts to get hot, the a/c will blow warm air. I have also noticed when the a/c is on the car seem to run rough. Runs just fine when the a/c is off (or not working).

Any suggestion.

Thanks!

Maj. Dundee

What is probably happening is the system is low on refrigerant the the compressor clutch is cycling on and off.

When the problem occurs, open the hood and look at the compressor clutch. If it spins, then stops and then spins, etc., you are low on refrigerant.

C.P.

I'll take a look at that, thanks!

C.P.

Okay, I added refrigerant to the system. It wasn't that low, but it did take some. The problem is still occurring. Is the compressor going bad?

Maj. Dundee

You never determined if the clutch is cycling on and off.

Doorman50

I also have a similar issue. I have a 1999 ML320. Two years ago, I had to get the compressor replaced ($$$$) and the evaporator valve overhauled. I live in a hot summer climate and when the temperature gets above 90, the A/C blows hot and cold air. What I mean by this is when driving on the highway or the engine is running at a driving speed, the AC works fine. When I am in traffic or at a light, it blows continually warmer. I can hear and feel the compressor cycle in and out. I have the equipment to check the freon as I suspected this also was the problem but it is ok. Any idea what the issue is? I suspect there may be some pressure switch that is not operating correctly but don't know enough to verify this.

Maj. Dundee

When this happens it means that your fan clutch is faulty and not spinning fast enough. It must be replaced.

Doorman50

Maj. Dundee, Many thanks. This is the second time you were right on for me with your problem diagnosis. I bought an OEM clutch on the Internet, the special spanner wrench and 36mm wrench and still have 3+ "C notes" in my pocket. I changed it literally in minutes. The most time consuming thing was cleaning the fan.

chris3815

Maj. Dundee, sorry to reopen this thread as I was reading a lot of the thread on here. I'm still confuse as I'm not sure how the compressor works. But when i look at the engine there is only one belt driving all the pulleys. So looking at the compressor I can't tell if it's working or not. I don't know what you mean the "clutch is cycling on and off". Can you point to a video demonstrating how it works?

Many thanks,

Maj. Dundee

Your compressor does not have a clutch which turns on and off. Everything is activated inside the compressor. Describe you problem.

Also PLEASE UPDATE YOU PROFILE in USER CP to include the year and where you live.

chris3815

Maj. Dundee

The aux. fans will only come on when certain criteria has been met.

The loud sound is probably coming from the main cooling fan because it is running at full speed. If that is the case, there is something wrong with the cooling system or there is a mechanical problem with the eng. & the ECM is reducing performance to protect the eng.

This part I do not understand............. the it doesn't accelerate as fast while AC is off like many have stated.

chris3815

Maj. Dundee

Do you have an idea why the fan clutch has to work more than needed.
During summer months my temp gauge would go up to almost 100c while idling! The two front fans would not come on.

The fan clutch runs at a higher speed because the clutch detects that the temp. is rising and therefore makes it run at a higher speed.

The aux. fans will not come on until the coolant temp. has reached 105°C on your temp gauge. According to you, the temp. is only at 100°C, so the aux. fans will not come. Do you understand?

chris3815

Thanks, I understand why the fans are not coming on.
Now back to the ac compressor. How do I know it's working properly? Last night, i tested the AC after driving home from work. When AC is on I can hear a slight change in noise near the AC compressor but not sure what it was. Thought it was the bearing on the pulley that has gone bad, but that sound only last for couple of seconds. So I decided to remove the serpentine belt and check to see if any of the pulleys are bad. All of them spins freely without any noise and resistant except the AC compressor. It has quite a resistance and kind if stiff for it to rotate. Is this normal or should it suppose to spin freely? Sorry for all the dummy questions. Thanks

Maj. Dundee

Contrary to popular belief all pulleys, except the A/C compressor, should have resistance when spinning them. The A/C pulley should be hard to spin.

Copy and paste these questions and type answers along side each one.

1. how long ago did this problem start?

2. did you replace all those parts to correct this problem?

3. do you own a scanner?

4. since the problem started, has the CEL come on?

5. what color coolant is in the expansion tank?

6. when you replaced the expansion tank, did you also get a new cap?

chris3815

Thank you for confirming the a/c compressor state.

1. how long ago did this problem start?
This noise,i just happen to hear it recently because i started to check why i keep hearing squeaking sound when backing off from the garage in the early morning. It only happens in the morning and afterwards it's all ok. Moving forward, there is no sound. I popped the rear brakes out to see if there are anything loose but everything was intact. I will check front brakes tonight and report back.

2. did you replace all those parts to correct this problem?
No, i replace all those parts due to temperature gauge keep fluctuating between 85c-100c over a year ago and it still does it till now. That is when i brought to the dealer and they say it's normal, but I don't trust them. I told them when I bought this car new it was always at 80c constantly no matter what what temperature outside was. But still the problem been like this for over a year. Still bugs me and I need help looking into this problem and don't want to drive my car in the summer in 90-100c weather.

3. do you own a scanner?
No, just ordered one and it will arrive in couple of days.

4. since the problem started, has the CEL come on?
No, CEL does not come on.

5. what color coolant is in the expansion tank?
Originally it was yellow, but the dealer sold me the MB blue color. After I've change it, I started to read further on the forum and found that I could of use Zerex G-05. But it's too late. Didn't want to switch it back.

6. when you replaced the expansion tank, did you also get a new cap?
Yes, I replace both expansion tank and a new cap as well.

5-6 months ago, I notice my car didn't have any cold Air when AC was on. After reading thru the forum, i went and bought a can of refrigerant and fill it up. I think i used up the can, but the air was cooler and I was happy but not as cold as before. I also hear some clicking noise inside the center console when turning it on then, but it seem to dissipate. Anyways, i think the engine is making loud noise due to cooling system as well, but unable to diagnose it. Any help is much appreciated.

Maj. Dundee

You seem to have two issues. The first is the A/C not working and with the last para. you typed about the clicking sound in the console means that the Blend Door Actuator Motor must be replaced. I will supply instructions for the blend motor.

But the second and more important issue is the engine performance and the temp. rising to 100°.

1. while the eng. is idling and at 100°, is there bubbling in the expansion tank?

2. while the eng. is idling and at 100°, check the hose at the expansion tank, pictured below, and see that every portion of the hose is hot to the same degree. Also check the hoses before and after at the Coolant Cir. Pump.

3. Depending on the answers above, it might be a good idea to change the Coolant Temp. Sensor.

4. and you still didn't answer this question.............. the it doesn't accelerate as fast while AC is off like many have stated. What does like many have said mean?

chris3815

Maj. Dundee

Hold on. I did not say to go ahead and replace the Blend Door. There are things that you have to check before replacing it.

What does like many have stated mean?

chris3815

Maj. Dundee

What about the results about the hoses and such in post #18?

chris3815

Maj. Dundee

None of these photo links will open.

You still haven't given the results of the question on the hoses and to be very honest with you, I'm getting tired of double checking on you to make sure you answer my questions.

chris3815