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BMW 528iA A/C-noise problems Pages: 12

TJJ on Sun May 18, 2008 2:38 PM User is offline

Year: 1999
Make: BMW
Model: 528iA
Engine Size: 2.8
Refrigerant Type: R134A
Ambient Temp: 50
Pressure Low: 29-32
Pressure High: 160-200
Country of Origin: Finland


I have a problem with under the dash (loudest at the passenger's side) bubbling and fluid rushing noises with my BMW 528 (E39 1999). It has a Denso 7SBU16C variable displacement compressor.

The (long) story goes like this: I went to a dealer to have the A/C-system checked and filled. It was fully working at this point...

My system should have 750 grams and it had 570 grams. I was not watching what they did, but they said that they filled the system, started the car and after a short time A/C-liquid was released via compressor's overpressure valve. Dealer then tried again to empty and fill the system but there was the same problem. After that they said that the receiver/dryer is blocked befause of moisture and needs to be replaced. Also the pressure sensor needed to be changed. I was charged for those, I wasn't very happy about this and suspected that an error was made by them.. They did not have the parts in stock, so the system was left empty for about a week (compressor was disabled), then the parts were installed, system vacumed and filled again and seemed to work.

But then I noticed those noises, they seem to be more evident when the weather is a little colder: I start the car, drive a few miles, stop to traffic lights and there is that bubbling sound. The noise stops when I switch the A/C off and starts again when the A/C is on (after a few seconds delay).

After that I contacted the dealer about the problem. They were not very helpfull but still refilled the system once again but it did not help.

Then I learned via another same shop's customer that the shop's equipments have been malfunctioning and putting in some cars way too much R134a that what they should have/what their filling machine shows. After some talks, the shop agreed to pay the receiver/dryer (overpressure probably broke it) and pressure sensor and they also changed expansion valve (but I did not actually see them doing the change) since it was thought that it's causing the noises.

But I still get the same noises and the dealer won't do anymore repairs saying now that it's a normal sound of this car
That was last summer and the situation is still the same.

I have now learned about how AC works and purchased pressure meters. I have noticed that the low side pressure is between 29-32psi (2,0-2,2bar) and the high side varies from 160-200psi (10-14bar). When high side goes to 200psi, electric fan starts and pressure drops to 160psi where the fan stops and pressure starts to slowly rise and the same cycle happens again. The cycle takes about 1-2 minutes, and happens even at low 50F temp. Car is idling at 700rpm. Is that normal for a variable displacement compressor? Or should it keep the pressures steady? I have also noticed that the fluid noises are there when the pressure rises but they stop few seconds after the fan starts and then start again after about 20-30 seconds. I haven't found much info about how variable displacement systems work in real life and what pressure range they use. I really don't understand what could cause this? Please help.

Karl Hofmann on Sun May 18, 2008 3:04 PM User is offlineView users profile

Early E39s had a two speed electric fan which ran all the time that the ac was on, switching to high speed when the pressure increased... Later models had a variable speed electric fan which would speed up and slow down as needed.. so I should check that this is working correctly ... Also check the main engine driven fan as the clutches do tend to fail..

Never knock on deaths door... Ring the doorbell and run away, death really hates that!

TJJ on Sun May 18, 2008 3:23 PM User is offline

The electric fan in my car is variable speed and seems to work correctly. But I'll have to diagnose that it actually works also at the lowest speeds and not just medium to high speeds. Main visco coupled fan is working correctly. But I think that even if the fan isn't working correctly, it doesn't explain the sounds I'm hearing (but it would explain the pressure raise cycle).

Karl Hofmann on Sun May 18, 2008 3:38 PM User is offlineView users profile

Normally a hissing in the dashboard area suggests that refrigerant vapour is passing through the expansion valve, suggesting that your refrigerant charge is low. A charge of 570 grams would not really affect the system at european temperatures... is the condenser clear and the fins not bent over?

Never knock on deaths door... Ring the doorbell and run away, death really hates that!

TJJ on Sun May 18, 2008 4:51 PM User is offline

It's not a hissing sound, it sounds like boiling water with occasional fluid moving sounds. The system is full. It was at 570g before all this trouble started. After that it has been recharged to 750g 3 times and still the same noise. So something was broken during the overfill and repairs. Condenser is clear without bend fins.

What would a dirty condenser do? Would it just cause high pressures or also something else? I'm still trying to understand how the system works...

bohica2xo on Sun May 18, 2008 5:01 PM User is offline

Well, something is not working correctly, and it is a condensing issue. That ugly boiling sound is poor quality / zero subcool liquid hitting the evaporator...

Your ambient temperature / high side pressure ratio is just plain awful. 200 psi @ 50f??? 4:1? Yikes! It is 100f ambient here right now. Park that BMW in the sun for an hour in my driveway, and you can expect it to cycle on the HPCO.

We look for ratios from 2.2:1 to 2.7:1, with 2.9:1 being barely acceptable for R12 cars converted to 134a.

Your viscous drive fan may well be bad, just because it spins somewhat is meaningless. See the FAQ's for fan clutch testing procedures. Check the air path through the heat exchanger stack. Small bugs will clog the fins deep, well below the surface. Use a drop light in the fan shroud after dark, and have a close look from the front of the car.


"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

Karl Hofmann on Sun May 18, 2008 5:12 PM User is offlineView users profile

A dirty condenser would increase your head pressure...

If the drier had been damaged though I cant see how a simple over charge could damage it, then this would mean that the desiccant will have been released in to the the system (It is normally held in the drier in a fabric bag and / or metal mesh.. If it had been released then it can collect in the next restriction that it comes to... the expansion valve, or possibly block the pipework leading up to the valve... feel the pipe along and see if there is a dramatic change in temperature between the drier and valve.. if so it would indicate a restriction there

Never knock on deaths door... Ring the doorbell and run away, death really hates that!

Edited: Sun May 18, 2008 at 5:14 PM by Karl Hofmann

TJJ on Sun May 18, 2008 6:11 PM User is offline

But I did not have any of these problems before the "service" so I think the problem is something else that just dirty condenser or poor fan. I'm not saying they are perfect, but I still think there is another problem. And the weird thing is that the noise problem is worse when outside temperature is low.

What about the compressor, if displacement control valve was damaged during the overfill and is not working (always at full power) wouldn't also that cause similar problems? Is there any way to verify this?

What about if the desiccant was released and is now blocking the expansion valve or tubing, what problem would that cause? Wouldn't a blocked expansion valve or tubing cause other problems i.e. freezing evaporator? There is no problem with that.

TJJ on Tue May 20, 2008 10:08 AM User is offline

I have now tested the electric fan, it works correctly and is variable adjusted between 10-100%. It runs at maybe 20% of full power power during the time it cools the AC condenser. The condenser was not dirty. I also checked the line between drier and expansion valve, there were no sudden temperature changes.

So what next? Does anyone know what happens if the compressor displacement control valve is not working correctly and is now locked in a fixed position?

Karl Hofmann on Tue May 20, 2008 5:52 PM User is offlineView users profile

I must admit that I have never come across a variable displacement compressor that is stuck in max displacement, but I guess that there ia a first time for everything..... It would entail replacing your compressor or at the very least a strip down and rebuild, but I have never stripped one of these compressors down..... I would be more inclined to take a closer look at your expansion valve..

Never knock on deaths door... Ring the doorbell and run away, death really hates that!

TJJ on Tue May 20, 2008 6:21 PM User is offline

What makes you suspect the expansion valve? What could I do to check it?

I actually have bought a new compressor, but I'm not sure if there is also something else wrong in the system. Since I don't have equipment to do the vacuum/refill, I'd like to make the system work correctly in one visit to an A/C-shop and not replace parts one by one and pay refill charges every time.

There may also be a problem with the new compressor... It's originally for BMW 740d. It's the same type etc. but I'm still wondering if it has different displacement pressure setting? Or are they all the same? Is it possible to adjust the setting? There seems to be an adjustment in the valve.

bohica2xo on Tue May 20, 2008 6:30 PM User is offline

I still think you are shopping for a unicorn.

If the condensor is clean, with good airflow there is no reason for those high side pressures. Even at maximum stroke with the proper charge, you could solder the TXV shut & not see that high side pressure.

Fixed displacment compressors run "wide open" all the time, and the result of a blocked TXV will be a low side in vacuum. If your compressor was stuck at full stroke, your low side would not be that high. Your low side says that the compressor & TXV are doing the job they were designed to do.

The high side pressures are a condensing issue, or a volume issue. Either half of that nice parallel flow condensor in your car is blocked internally, or you have 3x to 4x the proper oil charge & a full refrigerant charge crammed in it.

Check the condensor for warm or cool spots from top to bottom with your hand. If one section of parallel tubes is colder than the rest, you have a blockage - this is unlikely (unless some clown put sealer in it!), but easy to test without opening the system.

Given that the bozos (bellends) have overfilled the system repeatedly, there is no way to tell how much refrigerant & oil is in it without breaking it down. I would recover the system, and remove the receiver/dryer. Drill it & drain it. If you get more than two ounces of oil, time to flush everything to bare metal & start over.


"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

Karl Hofmann on Tue May 20, 2008 6:51 PM User is offlineView users profile

Must admit, that I am kinda clutching at straws with the TXV.... does the high side pressure drop if you spray a garden hose on to the condenser?

What this does is prove or discount that condenser air flow is the issue here...

Failing that possible air contamination of the refrigerant...

Never knock on deaths door... Ring the doorbell and run away, death really hates that!

TJJ on Wed May 21, 2008 1:38 AM User is offline

Thanks for the replys, I'm still trying to learn how the system works, so please have patience with me.

I'm now starting to see the light... It sure looks like there is something wrong inside the condenser. Sadly in this car it's hidden behind the electric fan/fan tunnel making it impossible to easily test it unless you remove the front bumber and the fan. But I'll do that soon and also clean the condenser at the same time.

The A/C-shop did not add oil, they used a Robinair machine and I have seen the printouts. I think there could be too little oil (because of the overfill and pressure release) but not too much.

There was talk (mechanics slipped this to the other customer, it was later partly verified and then denied completely) that the initial overfill was way over 750 grams, something like 1500 grams. Could that have caused the problem to the condenser? Or was the condenser already blocked and system worked without the evaporator noises only because the system was underfilled?

I'll do the garden hose test and see what happens.

Btw. as a final fix the A/C-shop (which is also an official BMW-dealer) asked advice from the BMW main dealer and said that they told to fill the system to 800 grams since that would fix the noises... I refused saying it would break the system.

bohica2xo on Wed May 21, 2008 2:26 AM User is offline

BMW's can be labor intensive in the heat exchanger area... The good news is that is not an expensive part - around 140 USD. same part number was used in a bunch of 5 series cars, the 2000 - 2003 M5 & the 2000 - 2003 M8.

The bigger question is, if it is clogged - what did it? anything that clogged the condensor had to pass through the compressor.

The expansion valve is a block type, and was used on a bunch of BMW vehicles - 5 series, M5, X5, Z8. Cost is about 42 USD. There are aftermarket replacments available for about half that (and maybe half the quality too).

The fact that your compressor makes 200 psi says good things about it's condition. Always good news to hear the most expensive part in the system may be ok.

Karl has a point, a lot of air in the system would raise pressures & reduce liquid quality. Doing the water spray on the condensor is a quick way to see how well the condensor is doing. If it drops like a stone, you know where the problem is.


"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

TJJ on Wed May 21, 2008 1:44 PM User is offline

I did the water spray test today:

Outside temp 52F

Initial values:
Lowside 30-32psi
Highside 150-200 (at 200psi electric fan started and dropped the pressure)

I sprayed water to the condenser, as I told earlier it's well covered so I can't spray the whole condenser, just some parts of it.

After few seconds highside pressure started slowly to go lower and stopped to 100psi and stayed there for maybe 3-4 minutes, lowside was still 30-32psi.

Then highside started to raise and went to 150, I noticed that viscous coupled fan started to spin at higher speed and highside dropped again to 100psi. Then pressure started to raise again and went to 160psi, again viscous fan started to spin faster and highside dropped to 105psi. Next highside went to 180 and viscous fan dropped it to 120psi. Electric fan was not running during this, it starts at 200psi. I sprayed again water and highside slowly dropped to 90psi.

So what do you think of the results? When the condenser was wet (4-5 minutes because of low outside temp), the system seemed to work as it should. Is it just dirty condenser or could internal blockage also behave this way?

I'll try to remove the front bumber next weekend and test condenser temperature differences and also clean it. Are there instructions of how to clean A/C-condensers? Maybe engine degreaser or something like that? I'm not sure if I can easily find a product made specially for this.

bohica2xo on Wed May 21, 2008 3:09 PM User is offline

Well, back to my first post. Airflow problem with the condensor. The water spray dropped the pressure ratio down to 2:1 from 4:1

Most likely a dirty air path. I have never been to Finland but if it anything like Manitoba, it is bug central during the warm months. Mosquitos, gnats, etc can really clog up a heat exchanger. The newer the car, the worse they plug up. Higher effeciency heat exchangers pack the fins in closer, and lean mfg. has made them thinner too.

Cleaning the air side of a condensor is best done with a good surfactant / solvent, and low pressure water. High pressure water can bend the thin fins over flat in an instant, and you will spend hours straightening them out...

I don't know if they sell a household cleaning product called "Simple Green" in Finland. A surfactant with butyl cellusolve, it dissolves bugs & oil well. Another product that we use is made by Zep, a heavy duty citrus based cleaner Zep Orange. Both are available in markets & home stores here in the USA. A similar product may be available to you.

A more industrial option is wax or floor stripper, which is used to clean floors before re-waxing. More caution is needed with this product, because it can de-gloss paint if you let it sit on the paint. Rubber gloves are recomended. It does clean very well.

No matter what solvent you use, the process is the same. Use a pump sprayer to soak the fins all the way through. Let it sit 5 to 10 minutes (do not let the cleaner dry on the condensor) then use a garden hose to flush out the debris. Repeat the process while the condensor is still wet, and the remainder should dissolve on thte second try.

This may mean removing a grille or bumper. I take the grille out of my pickup each spring and clean it this way.


"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

tomibriggs on Wed May 21, 2008 5:38 PM User is offline

If you need full access to your condenser, here the procedure.

Edited: Wed May 21, 2008 at 5:39 PM by tomibriggs

Karl Hofmann on Wed May 21, 2008 5:46 PM User is offlineView users profile

Because of all the plastic shrouds that surround the electric "Pusher" fan it is almost impossible to do a decent job of cleaning the condenser, you will find a lot of road compost jammed in between the fan motor and the condenser... By the time you have stripped off the front bumper, lights and so on to clean, it would make more sense to simply replace the condenser for the price that they are... Oh and check that the non return flaps are still attached to the shroud that surrounds the pusher fan.

Never knock on deaths door... Ring the doorbell and run away, death really hates that!

TJJ on Thu May 22, 2008 7:44 AM User is offline

bohica2xo: There are not so much mosquitos etc. over here that they would cause this. But the car was bought from Germany 4,5 years ago, I don't know how things are over there. But over the winter period here are lots of road salt and asphalt particles loosened by winter tires that may stuck to the condenser and then later collect dust. But the condenser doesn't look like it's blocked, but then again it may be impossible to see deep enough with all the stuff blocking the view.

Karl: It's not so easy to replace the condenser. First you have to remove the radiator and then the "cassette" where A/C-condenser is installed. But in the same cassette are also power steering and automatic gearbox radiators so you have to disconnect also those lines. Steering is not a problem, I actually just replaced a line and disconnected the tubes. But the gearbox is a big problem since it has "lifetime" fluids and I'd have to make sure that the level is still correct and that is done under the car with car running and gearbox at the right temperature etc. However, I intend to change the gearbox fluid soon, so once that is done, I may have more experience of this process (or I may have a broken gearbox..)

So, I think I will remove the bumper and the electric fan and try cleaning first. I may also at the same time remove the fan cowl and the viscous fan and try to see what things look like between the condenser and the radiator.

tomibriggs: thanks for the link, I already found another link, but this has better pictures. I do have BMW TIS program and Bentley books, but those only contain small b/w-pictures so DIY pages are good for extra info. I have removed the bumper few years ago to install headlight cleaners so I don't expect to have too much problems.

Karl Hofmann on Thu May 22, 2008 9:58 AM User is offlineView users profile

The E39 isn't too bad to do, just lots of silly plastic bits to take off... I have done a fair few condenser changes on this model and from memory I don't think that anything other than the condenser has to be disconnected.. The worst part of the job is putting the bumper back on when you are on your own, it is like trying to fit a big jelly... Once you have the fan cowl off you will see.

Never knock on deaths door... Ring the doorbell and run away, death really hates that!

TJJ on Thu May 22, 2008 2:08 PM User is offline

Still haven't taken off the bumper, but I did more visual checks with flashlight and the condenser looks clean. Lower part looks a little suspicious. I'm now a little afraid that cleaning will not help, but I'll still take the bumper off and also test for temperature changes.

So I have a few questions: How should the temperature change? From side to side? Does it drop evenly in all parts of the condenser? How much temperature drop should there be from condenser input to output?

bohica2xo on Thu May 22, 2008 2:33 PM User is offline

Oh, it's an awful-matic as well? Time to have a very close look at the heat exchanger package.

"Lifetime" fluids indeed. Maybe a short lifetime, but the fluid will last as long as the gearbox...

It is not just insects that can block the heat exchanger stack. Bird feathers, road dirt, pine needles... the list is endless. If you have reduced cooling & high head pressures in the A/C, then the transmission is running hot too. A second hand vehicle from another country? They could have lived down the road from a poultry farm, or had mice building a nest in the condensor stack.

If the condensor is that hard to get to, I agree with Karl - for 140 USD I would not put a 9 year old one back in.


"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

Karl Hofmann on Thu May 22, 2008 4:17 PM User is offlineView users profile

If you replace the condenser (Available in the UK for less than £70) then you will be able to see what has caught up in between the condenser and the radiator and you can clean the radiator off at the same time. Had a Jeep a couple of years ago that had a seemingly clean condenser until I took it off and saw that the rad was caked in road debris, preventing a huge amount of air flow

Never knock on deaths door... Ring the doorbell and run away, death really hates that!

TJJ on Fri May 23, 2008 2:19 AM User is offline

Condenser's price is not a problem. The problem is finding a place that listens to what I say and do the evacuation and filling correctly. Most places don't understand how the system works, they just plugin the hoses and do what the machine tells them. I sure don't want to experience another overfill...

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