Hi all,

Been lurking for a little while since have bought our second hand 08 GL 320 CDI.

In the last 3 weeks the A/C developed a weird behaviour, basically sometime it is blowing cool air and sometime it is not. Took it to a aircon expert and realise the freon was over filled. He has suck the extra out and currently it's in the correct amount/pressure now. He also check (by his machine that put in/suck out freon, as well as UV light) to make sure there is no leaking.

It is good for 1/2 a day but problem comes back. The guy was reluctant to work on MB cars so he refund my money and ask me to go elsewhere to seek help.

Then I have started this extended research on the reason behind it (including observing car of other brands). Tried to read material on how car A/C works. I have also been paying attention to see if this has a behaviour/pattern I can follow.

In summary the aircon will/will not blow cool air in the following situation:

1) If outside temperature (according to the car) is under 27c (80.6*F) it blows cool air. 28c to 30c (80.6*f - 86*f) it starts to struggle and above that it just blow hot air.

2) Keep in mind with #1, if I only turn on the front air vent it cools quite a lot better. Turn on the back vents it will really struggle (even at lower temperature). Again once it starts to blow hot air I will have to shut off the back try to "rescue" it but if outside temperature is too high there's nothing I can do.

3) If the car is running there is couple of things I can do to help the situation if it starts to blow hot air.

3a) I drive a road going down hill for an extensive amount of time (it will be fine if a flat road is follow, but as soon as it goes uphill slightly the A/C blow hot again)

3b) If I drive on free way for an extensive amount of time it will start to blow cool air again. But if there is some uphill going for longer distance it will blow hot again.

4) It seems cool air will only come effectively when I press on the Auto button as well as Mono button, and make sure every dials are on "16c". (Lowest temperature setting)

With above consideration, my assumption is: although nothing is leaking, it maybe is the A/C compressor is getting weaker (as not compressing as well as it should have)

I am thinking to get myself a re-manufacture unit locally for AUD$850. (The part number for Australian version is 002 230 5611 - which is something cannot be found in US.) I rang up the local dealer and they wanted AUD$3K!!

But before I commit to the purchase I would like to seek some 2nd opinions on what you guys think.

Thanks in advance for your advise.

 

I haven't had any issues with the a/c in my GL but in the last Jeep Grand Cherokee I had, had a similar problem.

Replaced the compressor with no effects, what it wound up being was an electric fan. It had two, one was temperature controlled to provide additional cooling like at idle, the other came on whenever the a/c was running to ensure sufficient airflow over the a/c condenser (mini radiator in front of radiator).

If the charge is right and the a/c clutch is engaging it is likely a bad/plugged condenser, bad fan or bad relay to the fan.

A simple check is to turn on the a/c to max cool and pop the hood open, the electric fan should be on. Mine is whenever the a/c is regardless of actual coolant temp.

A weak compressor might contribute to something like this but as its the most expensive part I'd exhaust everything else first or find a good indy MB shop that knows a/c well.

 

Thanks mrchris.

One more thing I forget to mention (which now I added back to my original post as point #4) is:

4) It seems cool air will only come effectively when I press on the Auto button as well as Mono button, and make sure every dials are on "16c". (Lowest temperature setting)

 

my guess is your ac fan fan/ relay is inoperable.

diagnose with das via the ac fan activation and follow the troubleshooting tree there. could be a fuse, a temp/ pressure sensor in ac, a fan relay or the fan motor - in that order

 

Thanks guys. Some good suggestions here.

I tried to google/youtube search on where is the fan relay but stumble. Is it something should be done by a professional or it can be check very easily?

 

alx, may I ask what is "das"?

 

Just some update.

Checked fan relay and the fan itself. All working.

No leaking what so ever, still can't figure out why... sigh.

 

I got the same problem. Did you find the solution to fix this. I came to the dealer for them to update softwere but it did not work. I came again and they said that AC controller is bad, I replaced AC controller but it did not fix the problem either.

 

It's winter here in Australia. So the aircon is not too much a problem. It is still temperamental thu.

May I ask: when the "hot air" comes in, was it damp/wet air? Or just dry air with wrong temperature?

 

Had same problem in another car and it was the aux fan. I havent looked in detail on the GL, but is there only one main fan? Or is there an aux?

 

I got the air from the outside not dry air. I got E350 also, and I just exchange ambient sensor for my GL450 but I do not think it fix my problem.

 

Could you please let me know what is the engine temperature when you car running? Mine is about 94-96 C. My E350 is about 91-92 C. Not sure if this difference make my AC intermittant working

 

Just got another air-con guy to check the system.

Long story short, the problem still not fixed, but he found out I had a little bit too much gas in the system so he make sure the pressure is correct. Problem still persist but it's getting better.

Nothing is leaking in my aircon system.

As far as I concern there is only 1 fan. Which is the one in the radiator.

 

Seems like this is the second time they said you had too much Freon.


That makes me wonder how they are testing. If by weight, where is it coming from OR (more likely) do they know the proper amount it should have.


If they are checking by pressure, then you want to know why it is running high, and is it high on both sides.

 

Quick update - I think it has something to do with the battery.

I never got a chance to solve the problem but lately it is getting worst. Recently I took the car to do the routine service and have been told the battery is dying and need a new one.

So I replace the battery and I go for the one with bigger "ACC" figure (900 ACC... whatever that means)

Suddenly the aircond has been working much better. Still have the temperamental when going up/down hill but it is more "livable" now.

Maybe this is where I should be start looking at.

 

Has anybody looked at the evaporator coil? It might be dirty.

 

Where is the evaporator coil lives?

 

Hi all,

Problem has been resolved.

The electronic valve at the a/c compressor is not working correctly.

I could have just replace the valve (AUD$800) but I have opted to replace the entire compressor (AUD$1900 instead) to save myself from possible future problem.

Just let you guys know what has happen ever since.

 

Good to know. My AC is acting up again. Thank god for extended warranty..