BMW A/C Woes

CBC on Tue August 02, 2005 9:55 PM

Year: 1995
Make: BMW
Model: 525i
Engine Size: 6 cyl
Refrigerant Type: R134
Ambient Temp: 85
Country of Origin: United States

My BMW is at the repair shop having major A/C work done. So far, the compressor, evaporator, and other associated parts have been replaced with new ones. The system was also flushed. The repair shop has verified that the new components are working correctly and the system pressure is correct. However, they are concerned that the temp at the vents is not cold enough. They are currently getting a readiing of 61 degrees, but believe it should be more like 55 degrees. I am by no means questioning their work and for a $1,700 repair bill, I appreciate the extra attention to detail. Does 61 degrees at the vents seem acceptable or is 55 more what is to be expected? If everything is working correctly and as intended, what reason(s) could there be for not getting that extra 5 degree drop in temperature? Thanks!

Edited: Tue August 02, 2005 at 10:41 PM by CBC

zimaad on Tue August 02, 2005 10:21 PM

possible that cooling fans aren't coming on correctly??

brickmason on Tue August 02, 2005 10:35 PM

The volume of airflow from the vents has a lot to do with vent temps.

In other words, a 61 degree vent temp with a flow of air like a cyclone will cool the interior much faster than a 40 degree vent temp with poor air flow.

What is the vent temp on low fan?

-------------------------
Just another brick in the wall

Had a little mule I fed him castor oil and every time he jumped the fence he fertilized the soil

CBC on Tue August 02, 2005 10:42 PM

Thanks for the feedback. I'll have the shop check this.

CBC on Tue August 02, 2005 10:50 PM

Thanks. Not sure if they are measuring the vent temp on low or high (or somewhere in between). I know this system has the auto climate control and I made sure the shop realized they would need to put the fan speed on a setting between 1 and 5, instead of letting the system determine the air output. I'll ask the shop what the vent temp is on the low fan speed. I thought 61 degrees seemed acceptable, given that it was 95+ outside today. However reading a few other posts this evening, I see that some individuals get vent temp readings in the mid 40 degree range.

Thanks for the help and I'll let you know what reading they get on low speed.

riphip on Tue August 02, 2005 10:57 PM

Maybe the shop should check the temps while driving it. Would be forcing more air over the condenser.
Rick

brickmason on Tue August 02, 2005 11:03 PM

Ambient is measured 2 inches from the condenser.

The temp drop from condenser to evaporator should be approximately 30 to 35 degrees.

So remember that to get 40 degrees at the vent would require an ambient of 70 to 75 degrees at the condenser.

Does the interior seem to cool comfortably within 15 minutes or so when the cabin is over 100 degrees?

-------------------------
Just another brick in the wall

Had a little mule I fed him castor oil and every time he jumped the fence he fertilized the soil

CBC on Fri August 05, 2005 11:18 AM

Update on my progress. The repair shop was able to get 48 deg at the vents on low fan speed. All seemed to be ok, until driving yesterday (95+ temp). System began blowing "luke cool" air from time to time, and the vent temp seemed to stay warmer than it should be - never really returning to what would be expected of a properly functioning system. Also did notice any water dripping from under the car. It did finally leave a puddle of water after sitting in the driveway for a short time. Back in the shop this morning. They are going to evac the system again and recharge. Also will check the engine fan clutch as well. On the drive there this morning, the system seemed to be cooling perfectly, but the outside temp was only 68 deg.

Could the system be freezing up, or should I suspect problems with the vent doors or something? The higher the fan speed, the warmer the air. The volume seems to be consistent.

Thanks

bohica2xo on Fri August 05, 2005 12:51 PM

That BMW has a "highly developed" A/C system, with 5 sensors & a complicated control system. They are capable of good cooling, and usually work well.

The biggest problem with the system is the "Microfilter" or cabin air filter. It must be changed on a regular basis, or the ventilation system does not work properly. This would not be a problem if you could change the filter easily.

On the 525's, the microfilter is a real SOB to get to. You have to remove the glovebox, trim panel, passenger footwell trim panel, an air duct, the A/C control unit, and then the microfilter cover unclips. So, the filter rarely gets changed. I believe BMW specifies a 15k change on the filter.

There are a couple of other items that can affect cooling too.

There are 2 water control valves in that car. They are electrically operated, and their condition is normally open. So, a broken wire, or connector that falls off will open the valve. The Climate Control computer will record this as a fault, but does not have a warning light. The fault codes can only be read with a scan tool. The water valves can also freeze in the open condition. When this happens, the computer will not see a fault, since the valve coil has no position sensor.

The condensor fan is controlled by the "medium pressure switch". The fan runs at "speed 2" when the high side goes over 257 psi, and the fan shuts off below 213 psi. The fan is controlled by two relays, and has a resistor for low speed operation. If the resistor fails, the fan will not run in low speed, causing poor A/C performance. No fault will show on the scan tool. If either relay fails, the fan will fail to operate in the mode controlled by that relay - again, no fault will show on the scan tool.

Relpace the Microfilter first, unless it is less than 15k miles old. Then check the pressures and fan operation. Check pressures at 2000 engine rpm, with the fan on high, doors closed and recirculate air. Run the engine at 2000 rpm for ten minutes, and check the pressures while it is still at speed. At 80f ambient, 50~70% humidity, you should see:

164~215 psi High side

36~43 psi Low side

The condensor fan should be running at low speed, perhaps even high speed during the test.

.

-------------------------
"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.

CBC on Fri August 05, 2005 2:13 PM

Thank you very much for the information. Ironically enough, I am now taking my 525i to BMW for diagnosis. The original repair shop verified the following symptoms and consulted with the BMW dealer service center. - On Low fan speed, the vent temp is 45 deg. On speed 2, the temp rises to 55 deg. speed 3 it goes to around 70 deg., and on high speed the vent temp rises to about 80 deg. BMW said the problem is with the HVAC control panel. From your description of the microfilter , I am wondering if this might well be the problem - Higher vent fan speeds equating to higher vent fan temps.

Being the second owner, I do not have any documentation on when the microfilter might have been replaced. I am going to assume the worst and figure it has more than 15K on it. Is the microfilter replacement something a person with average mechanical skills (I can replace water pumps, alternators, etc.) can accomplish? Are there any special tools required, and can you recommend a service manual I can purchase that would guide me through the replacement process?

Thanks again for the advice.

Karl Hofmann on Fri August 05, 2005 2:32 PM

The E34 does suffer from water passing the water control valves, adding heat to the cabin air, it may be worth clamping the heater hoses to see if the situation improves, 61F is nowhere near good enough. I feel that if it was a fan issue, then the situation would improve when you were on the move.

Bohica, I know what you mean about the cabin filter, mine has to come out from the drivers side around all the added electrical nonsense that controls the 4WD system

CBC replacing the cabin filter is more a case of patience rather than technical abillity, the replacement filters are hinged in the middle to make it easier to slide the new filter in.

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

Edited: Fri August 05, 2005 at 2:37 PM by Karl Hofmann

CBC on Fri August 05, 2005 5:39 PM

Your water valve idea may well be it. I have noticed that warm air seems to "trickle" from the floor vents sometimes. Coolish air from the dash vents and warmish air from the floor, with the temp controls set to the coldest settings. Are these valves under the dash or in the engine compartment? Any estimate on how difficult these would be to replace, and are there only two? I had a 280ZX that had the same problem in college and I remember needing to be double-jointed to get under the dash to the valve!

Any theory on why the vent temp gets warmer as the fan speeds increase? 45 deg on speed 1, 80 or so on speed 4.

I ordered a BMW repair and service CD, and will try to further diagnose and repair the problem with that and help from you guys!
Thanks

Edited: Fri August 05, 2005 at 5:42 PM by CBC

Karl Hofmann on Fri August 05, 2005 5:52 PM

Those valves are easy to get at as they are under the bonnet, up near the bulkhead, and in the UK not too dear to replace. I'll take a photo of the valves on my car tomorrow an post it up for you to have a look at.

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

bohica2xo on Fri August 05, 2005 6:33 PM

CBC:

An Alldata subscription for that car would be a good manual. Like Karl says, the microfilter replacement is just tedious - no special tools, just 3 pages of pictures and instructions in the manual.

The water valves would be suspect if you have poor cooling on the highway, where the fan is not doing much.

The blend door is electro-mechanical, and if you can select hot to cold, it is working. The system will store codes if the actuator is bad.

Having the codes read by the dealer will eliminate (or pinpoint) any electrical problems. If the condensor fan appears to have both speeds, you can cross that one off the list. That leaves the water valves.

As a side note, I have seen more than one beemer with the original microfilter still in place at the 60k mile service - even though the car had been serviced regularly. Learning to change your own is the best way to know it really got done.....

.

-------------------------
"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.

CBC on Sat August 06, 2005 9:17 PM

Thanks Mr. Hofmann. I'll watch for the photos and then find the valves on my car.

Karl Hofmann on Sun August 07, 2005 5:37 AM

Here are the photos with the location of the water valves on the E34

the plastic covere may be stiff to remove, but is only held on with three spring clips

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

Edited: Sun August 07, 2005 at 5:51 AM by Karl Hofmann

CBC on Sun August 07, 2005 10:23 PM

Thanks Mr. Hofmann. Using your photos, I found the heater valves on my car immediately! Ironically, my car does not have a plastic cover to remove. I guess that has long since been lost by a previous owner. I ordered a new valve this afternoon and hope to receive it by Thursday or Friday. I'll let you know how it turns out.

CBC on Sun August 07, 2005 10:29 PM

Thanks for the info. The system does seem to blow much warmer air at highway speeds. In fact, it blows hot air (not outside air temp)from the lower vents at decent speed, while the dash vents blow air that is around 80 degrees or so. Even with the temp controls set to their coldest settings. I ordered a new valve, and microfilter today as well as a subscription to ALLDATA. Thanks for the tip! I'll let you guys know how this turns out when I make the repairs later this week.

CBC on Thu August 11, 2005 12:01 PM

Repair Update: Replaced the water valves this morning. It did seem to improve the temp at the vents significantly throughout all fans speeds. It is 69 degrees outside this morning, so I'll know for sure when we hit the 90's again. One issue still remains however. Of the center vents (just above the radio), the right side vent (passenger) does not blow air as cold as the left side vent. The left vent is cold, the right is cool. Is this a problem with a mixer door not closing all the way, or maybe a sensor that is located in the HVAC control panel? Any help is certainly appreciated. Thanks!

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