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E39 (1997 - 2003)
The BMW 5-Series (E39 chassis) was introduced in the United States as a 1997 model year car and lasted until the 2004 when the E60 chassis was released. The United States saw several variations including the 525i, 528i, 530i and 540i. -- View the E39 Wiki

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  #1  
Old 09-20-2010, 12:20 AM
GreenTiger GreenTiger is offline
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Weird AC Prob....Need help diagnosing

Hello everyone...pretty frustrated about this issue. I have a 1998 540i build date 7/98 (because AC compressor changed around this time, and maybe this is a significant piece of info). So i turn my AC on full blast, fan works fine (final blower unit intact), turn on AC, I hear a click and the engine revs lower for sec so the compressor is engaging. The fan also turns on right away when the AC is turned on..so that is okay. Refrigerant 134a is full at 32 PSI, so no leaks. BUT warm air blows out...warmer than ambient temperature Whats going on??
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  #2  
Old 09-20-2010, 06:37 AM
bubbs92 bubbs92 is offline
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I have the same problem only when the car is sitting in the sun for awhile. After a few minutes of running the engine the air would eventually get cold.
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  #3  
Old 09-22-2010, 01:03 PM
rdl rdl is online now
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Quote:
Originally Posted by King540i View Post
Hello everyone...pretty frustrated about this issue. I have a 1998 540i build date 7/98 (because AC compressor changed around this time, and maybe this is a significant piece of info). So i turn my AC on full blast, fan works fine (final blower unit intact), turn on AC, I hear a click and the engine revs lower for sec so the compressor is engaging. The fan also turns on right away when the AC is turned on..so that is okay. Refrigerant 134a is full at 32 PSI, so no leaks. BUT warm air blows out...warmer than ambient temperature Whats going on??
I have a 530i so not familiar with your car. But I've suffered A/C problems on other cars and learned some things you might check.

1 are you using a thermometer to determine the vent air is warmer than ambient? I've found the 5 finger thermometer to be unreliable for that comparison. If vent air is truly warmer, the problem is probably the HVAC air distribution box sending warm air while blocking off cooled air - the evaporator could be cold but none of that air is sent to the vents. If so, it could be duct temp sensors, motors driving the flappers. Come to think, I've had this happen with A/C working great but vent air only a little cool when should have been icy.

2 It sounds as though the compressor starts, but does it for sure & then continue to be engaged? There are pressure switch(es) that will disengage the compressor for out of spec conditions. Look at the compressor with HVAC calling for cold air and verify that the center hub is turning; the grooved, outer pulley always turns with the belt, the A/C clutch engages to turn the hub that turns the compressor only when the HAVC call for cold. If not, hope for a broken wire, plug off, blown fuse, bad relay. If you can get to it, does the lead to the A/C clutch have 12V on it which is used to engergize the clutch - not all the time, only when HVAC calling for cold.

If it's a weak/failed A/C clutch, bad pressure sensor/switch or low refrigerant you'll need an A/C shop with specialized equipment.

3 Quick and dirty check if compressor is circulating refrigerant. If if you can get your hand on the hoses in & out of the compressor (anywhere: at compressor, near firewall, into condenser, etc.) the large one should be cold and the small one hot - the finger thermometer works just fine for this! If not, the compressor is not compressing, the refrigerant charge is too low, or there is a blockage in the system.

If you get this far, you're probably going to have to go to a shop with A/C test & repair equipment.

4 With A/C gauge set, check high side and low side pressure while the compressor is running. TSI specs for '98 540 expansion valve are 1.8 bar exit (low side, bigger hose, into compressor) and 14 bar input (high, smaller hose, out of compressor to condenser then evaporator) side. Conversions are 27 psi and 210 psi. If your pressures are close to these you should get cold air, subject to point 1 above. Unless, your expansion valve in the evaporator is bad, other blockage in sytem, etc.

4 the 32 psi you see does not prove the system has a full charge of refrigerant, only that some refrigerant is present - could be low or full charge. Compare to a gas grill propane tank. The pressure going to the regulator is pretty much constant from a full tank until it is empty at which point it plunges to zero as the last bit of liquid evaporates. Same for A/C refrigerant. Even some R134a is actually semi-good news. It means that if you do have a leak and therefore low refrigerant, at least it hasn't gone so low that air and moisture are into the system, which would be maxi-bad news.

The certain method to determine refrigerant charge is evacuate the system and weigh the refrigerant removed. This requires specialized $$$ equipment, of course. An alternative is to check pressures on a hot humid day when A/C is heavily loaded to make cold air. A pressure check on a day only warmish and dry does not load the system and can give good reading even if the A/C charge is low. I realize that unfortunately you can't do this test, sorry.

For the picky people: there are curves/tables that adjust target pressures for ambient temp & humidity. I haven't found them for any of the BMW models.

Hope all this helps. Good luck.
RDL
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  #4  
Old 09-22-2010, 01:48 PM
rdl rdl is online now
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Quote:
Originally Posted by bubbs92 View Post
I have the same problem only when the car is sitting in the sun for awhile. After a few minutes of running the engine the air would eventually get cold.
The TIS calls for evaporator temp sensor (i.e. vent air temp, pretty much) reading <15C/59F after 3-4 minutes starting from 50C/122F interior temp, HVAC in recirc mode, engine normal operating temp, at idle speed. If this test fails, TIS recommends first checking refrigerant fill. Only then check other potential faults.

By way of comparison, my 530 delivers cold air in less than one minute, down to 45-47F in 2 or 3 minutes, HVAC in automatic, at ambients 80F+ after a sun soak.

Regards
RDL
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  #5  
Old 09-22-2010, 02:18 PM
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bmw_n00b13 bmw_n00b13 is offline
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I guess you've ruled out the centre dash adjustment and set the temp to < ambient?
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  #6  
Old 09-22-2010, 05:55 PM
GreenTiger GreenTiger is offline
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Quote:
Originally Posted by rdl View Post
I have a 530i so not familiar with your car. But I've suffered A/C problems on other cars and learned some things you might check.

1 are you using a thermometer to determine the vent air is warmer than ambient? I've found the 5 finger thermometer to be unreliable for that comparison. If vent air is truly warmer, the problem is probably the HVAC air distribution box sending warm air while blocking off cooled air - the evaporator could be cold but none of that air is sent to the vents. If so, it could be duct temp sensors, motors driving the flappers. Come to think, I've had this happen with A/C working great but vent air only a little cool when should have been icy.

2 It sounds as though the compressor starts, but does it for sure & then continue to be engaged? There are pressure switch(es) that will disengage the compressor for out of spec conditions. Look at the compressor with HVAC calling for cold air and verify that the center hub is turning; the grooved, outer pulley always turns with the belt, the A/C clutch engages to turn the hub that turns the compressor only when the HAVC call for cold. If not, hope for a broken wire, plug off, blown fuse, bad relay. If you can get to it, does the lead to the A/C clutch have 12V on it which is used to engergize the clutch - not all the time, only when HVAC calling for cold.

If it's a weak/failed A/C clutch, bad pressure sensor/switch or low refrigerant you'll need an A/C shop with specialized equipment.

3 Quick and dirty check if compressor is circulating refrigerant. If if you can get your hand on the hoses in & out of the compressor (anywhere: at compressor, near firewall, into condenser, etc.) the large one should be cold and the small one hot - the finger thermometer works just fine for this! If not, the compressor is not compressing, the refrigerant charge is too low, or there is a blockage in the system.

If you get this far, you're probably going to have to go to a shop with A/C test & repair equipment.

4 With A/C gauge set, check high side and low side pressure while the compressor is running. TSI specs for '98 540 expansion valve are 1.8 bar exit (low side, bigger hose, into compressor) and 14 bar input (high, smaller hose, out of compressor to condenser then evaporator) side. Conversions are 27 psi and 210 psi. If your pressures are close to these you should get cold air, subject to point 1 above. Unless, your expansion valve in the evaporator is bad, other blockage in sytem, etc.

4 the 32 psi you see does not prove the system has a full charge of refrigerant, only that some refrigerant is present - could be low or full charge. Compare to a gas grill propane tank. The pressure going to the regulator is pretty much constant from a full tank until it is empty at which point it plunges to zero as the last bit of liquid evaporates. Same for A/C refrigerant. Even some R134a is actually semi-good news. It means that if you do have a leak and therefore low refrigerant, at least it hasn't gone so low that air and moisture are into the system, which would be maxi-bad news.

The certain method to determine refrigerant charge is evacuate the system and weigh the refrigerant removed. This requires specialized $$$ equipment, of course. An alternative is to check pressures on a hot humid day when A/C is heavily loaded to make cold air. A pressure check on a day only warmish and dry does not load the system and can give good reading even if the A/C charge is low. I realize that unfortunately you can't do this test, sorry.

For the picky people: there are curves/tables that adjust target pressures for ambient temp & humidity. I haven't found them for any of the BMW models.

Hope all this helps. Good luck.
RDL
I really appreciate your help rdl. Low and behold, I found out that my problem was that I had the center vent setting on 2 RED dots the whole damn time. So I took it out for a drive, put it on 3 blue dot/ 2 blue dots and started to get cool air. But even after about 15 mins of running, the air stayed cool but did not get icy cold. You said, this might be due to a duct temp sensor? Is that the thing that takes the temperature of air being sucked back into the AC system for inside the cabin? Also, you said a 98 540i needs to be at 27PSI? I realize that this is not a good way to measure refrigerant levels, but vacuuming out all refrigerant and putting in exactly 775g of refrigerant is an expensive process if I take it to a HVAC guy. Also I suspent that at 33PSI my system is slightly overcharged b/c when I turn on the AC, I can hear the compressor as if it is struggling, like a wshhhh wshhh constant cycle. I am going to bleed some R134a off and see what happens. What do you think rdl?
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  #7  
Old 09-22-2010, 09:15 PM
rdl rdl is online now
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Quote:
Originally Posted by King540i View Post
I really appreciate your help rdl. Low and behold, I found out that my problem was that I had the center vent setting on 2 RED dots the whole damn time. So I took it out for a drive, put it on 3 blue dot/ 2 blue dots and started to get cool air. But even after about 15 mins of running, the air stayed cool but did not get icy cold. You said, this might be due to a duct temp sensor? Is that the thing that takes the temperature of air being sucked back into the AC system for inside the cabin? Also, you said a 98 540i needs to be at 27PSI? I realize that this is not a good way to measure refrigerant levels, but vacuuming out all refrigerant and putting in exactly 775g of refrigerant is an expensive process if I take it to a HVAC guy. Also I suspent that at 33PSI my system is slightly overcharged b/c when I turn on the AC, I can hear the compressor as if it is struggling, like a wshhhh wshhh constant cycle. I am going to bleed some R134a off and see what happens. What do you think rdl?
The red/blue dot dial is interesting. On my '03 that dial has no noticable effect when the HVAC is delivering cool air. It works quite nicely when delivering heat. I wonder if that is a design change between the model years, or that mine doesn't function properly?
BMW N00b13 hit it on the head, didn't he?

Perhaps you're satisfied now? If so, feel free to ignore the following.
Except - DON'T BLEED OR VENT ANY REFRIGERANT unless you have other reasons for believing your system is overcharged.
Even then you should take it to an A/C shop, since R134a is a green house gas. They might remove the excess in return for you donating it to them?

The 1.8 bar / 27 psi is the TSI spec while the compressor is running. Is that how you measured it? If the compressor is not running, the R134a pressure is a function of its temperature. The 32 psi you measured would simply be the the pressure for the temperature of the R134a when you took the reading. As I described in my earlier post, it is in no way, shape or form an indication of the mass of R134a in your system. The 32 psi says only that some refrigerant is there - which is good.

The duct temperature sensors I refered to are measuring vent output temps. The HVAC monitors cabin temp & decides what temp air to blow out the vents. It then moves flaps to vary the amounts of evaporator and heater core air until the duct temp sensor reports the target temperature. The target duct temp will change over time. For instance when I start my car baked by a sun soak, the cabin temp will be >90F++ while my set point is 70F. HVAC blows air as cold as it can get, apparently 45F. As the cabin approaches the set point temp, the vent temp is increased - to around 60F - still cool but not icy. This makes sense since one wants reasonable air flow through the cabin, but wouldn't want to be turned into a popsicle with a 45F breeze.

Diagnosing whether a false sensor reading is causing a problem requires a diagnostic code reading system; a BMW dealer or independant with a BMW capable system. Or troll through this forum for BMW diagnostics and learn to do it yourself.
http://forums.bimmerforums.com/forum...play.php?f=233
You can get the software off the internet & the cable to connect to the car can be bought for $30 to $50.

The 15 minute ramp up to only cool temperatures is consistent with a low charge, but several other problems too. But, a rule of thumb is that even a good A/C system will seep about 20 grams of R134a / year. Assuming your car hasn't been recharged since new, one would expect to be down a significant % of the factory charge.

An overcharge will not degrade cooling. A large enough overcharge will though ruin the compressor when liquid refrigerant is sucked into the cylinders and causes hydrolock. Hydrolock would generate a big bang and then lots of noise! If it hasn't happened yet, you're almost certainly not overcharged.

Based on what you've described, it seems more likely that your system is low on refrigerant. In my travels in the US, I've found that many of the auto parts stores will loan or rent equipment cheap & often help to do a test in the parking lot. I'd try to scrounge up a set of A/C gauges and check pressures on your running system. Google for A/C pressure interpretation. Here's a good starting point
http://www.autoacrepairs.com/index.html

Assuming the results are consistent with a low charge, & if it were my car I'd buy an R134a charge kit and try adding some to the system - VERY SLOWLY AND CAREFULLY.

ALL THE SUGGESTIONS BELOW ARE AT YOUR OWN RISK. YOU WILL RUN THE RISK OF OVERCHARGING YOUR SYSTEM AND DESTROYING THE COMPRESSOR.

In making these suggestions, I'm assuming that the car has delivered much cooler A/C air than it is now. Some cars simply don't have really cold A/C. I've no idea if a '98 540 falls into this category. Also I don't know what your vent temp is. If the car is new to you, check around to find what vent temp you should expect. Adding refrigerant to a system that is already delivering as cold as it can, could easlily result in overcharging.

I'm also assuming that refrigerant hasn't been added recently, i.e. that the system is not overcharged now, and that poor cooling is caused by some other fault.

First buy or borrow a $10 to $20 food thermometer, the kind that reads say -20F to 220F in 2 deg increments. But not a meat thermometer, they aren't accurate enough and the range is wrong. Check it in a glass full of ice & water for a reading of 32F - adjust if necessary. Confirm that your lowest vent temp really is >60F

Then:

1 check that the condenser is not plugged up with leaves &/or bugs. Also check that the fan in front of the condenser turns on when the A/C has been running for a while.
2 put the thermometer in the vent
3 turn HVAC to minimum temp point and fan on medium, or to A/C MAX if you have that option & vent dial to 3 blue dots. Give it say 10 minutes to let the vent temp stabilize
4 follow the R134a kit's instructions and add say 100g to your A/C - you can guess by the cold/warm level in the can changing or what % lighter it feels.
5 wait 5 minutes and see what happens to the vent temp, rev the engine up to 2,000 RPM so that the compressor has lots of speed to do it's job. Any higher is a waste.
6 check that the compressor clutch is engaged, i.e. the hub is spinning
7 repeat 4 to 6 until you get to a vent temp you can live with, say 59F as noted in the TIS
7 if 200 to 250 grams doesn't improve the vent temp, I'd stop immediately since that should be more than enough to make a difference unless your A/C has other problems.
8 Otherwise, continue but stop at 500g since your system must have a at least ~200 grams to be cooling at all - the total then would be ~700 g. You don't want to increase your risk of overcharging to the point of hydrolock.

Hope this helps. Otherwise, I'm afraid it's time to go to a shop with A/C expertise.

Good luck

RDL
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  #8  
Old 09-22-2010, 09:58 PM
GreenTiger GreenTiger is offline
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Quote:
Originally Posted by rdl View Post
The red/blue dot dial is interesting. On my '03 that dial has no noticable effect when the HVAC is delivering cool air. It works quite nicely when delivering heat. I wonder if that is a design change between the model years, or that mine doesn't function properly?
BMW N00b13 hit it on the head, didn't he?

Perhaps you're satisfied now? If so, feel free to ignore the following.
Except - DON'T BLEED OR VENT ANY REFRIGERANT unless you have other reasons for believing your system is overcharged.
Even then you should take it to an A/C shop, since R134a is a green house gas. They might remove the excess in return for you donating it to them?

The 1.8 bar / 27 psi is the TSI spec while the compressor is running. Is that how you measured it? If the compressor is not running, the R134a pressure is a function of its temperature. The 32 psi you measured would simply be the the pressure for the temperature of the R134a when you took the reading. As I described in my earlier post, it is in no way, shape or form an indication of the mass of R134a in your system. The 32 psi says only that some refrigerant is there - which is good.

The duct temperature sensors I refered to are measuring vent output temps. The HVAC monitors cabin temp & decides what temp air to blow out the vents. It then moves flaps to vary the amounts of evaporator and heater core air until the duct temp sensor reports the target temperature. The target duct temp will change over time. For instance when I start my car baked by a sun soak, the cabin temp will be >90F++ while my set point is 70F. HVAC blows air as cold as it can get, apparently 45F. As the cabin approaches the set point temp, the vent temp is increased - to around 60F - still cool but not icy. This makes sense since one wants reasonable air flow through the cabin, but wouldn't want to be turned into a popsicle with a 45F breeze.

Diagnosing whether a false sensor reading is causing a problem requires a diagnostic code reading system; a BMW dealer or independant with a BMW capable system. Or troll through this forum for BMW diagnostics and learn to do it yourself.
http://forums.bimmerforums.com/forum...play.php?f=233
You can get the software off the internet & the cable to connect to the car can be bought for $30 to $50.

The 15 minute ramp up to only cool temperatures is consistent with a low charge, but several other problems too. But, a rule of thumb is that even a good A/C system will seep about 20 grams of R134a / year. Assuming your car hasn't been recharged since new, one would expect to be down a significant % of the factory charge.

An overcharge will not degrade cooling. A large enough overcharge will though ruin the compressor when liquid refrigerant is sucked into the cylinders and causes hydrolock. Hydrolock would generate a big bang and then lots of noise! If it hasn't happened yet, you're almost certainly not overcharged.

Based on what you've described, it seems more likely that your system is low on refrigerant. In my travels in the US, I've found that many of the auto parts stores will loan or rent equipment cheap & often help to do a test in the parking lot. I'd try to scrounge up a set of A/C gauges and check pressures on your running system. Google for A/C pressure interpretation. Here's a good starting point
http://www.autoacrepairs.com/index.html

Assuming the results are consistent with a low charge, & if it were my car I'd buy an R134a charge kit and try adding some to the system - VERY SLOWLY AND CAREFULLY.

ALL THE SUGGESTIONS BELOW ARE AT YOUR OWN RISK. YOU WILL RUN THE RISK OF OVERCHARGING YOUR SYSTEM AND DESTROYING THE COMPRESSOR.

In making these suggestions, I'm assuming that the car has delivered much cooler A/C air than it is now. Some cars simply don't have really cold A/C. I've no idea if a '98 540 falls into this category. Also I don't know what your vent temp is. If the car is new to you, check around to find what vent temp you should expect. Adding refrigerant to a system that is already delivering as cold as it can, could easlily result in overcharging.

I'm also assuming that refrigerant hasn't been added recently, i.e. that the system is not overcharged now, and that poor cooling is caused by some other fault.

First buy or borrow a $10 to $20 food thermometer, the kind that reads say -20F to 220F in 2 deg increments. But not a meat thermometer, they aren't accurate enough and the range is wrong. Check it in a glass full of ice & water for a reading of 32F - adjust if necessary. Confirm that your lowest vent temp really is >60F

Then:

1 check that the condenser is not plugged up with leaves &/or bugs. Also check that the fan in front of the condenser turns on when the A/C has been running for a while.
2 put the thermometer in the vent
3 turn HVAC to minimum temp point and fan on medium, or to A/C MAX if you have that option & vent dial to 3 blue dots. Give it say 10 minutes to let the vent temp stabilize
4 follow the R134a kit's instructions and add say 100g to your A/C - you can guess by the cold/warm level in the can changing or what % lighter it feels.
5 wait 5 minutes and see what happens to the vent temp, rev the engine up to 2,000 RPM so that the compressor has lots of speed to do it's job. Any higher is a waste.
6 check that the compressor clutch is engaged, i.e. the hub is spinning
7 repeat 4 to 6 until you get to a vent temp you can live with, say 59F as noted in the TIS
7 if 200 to 250 grams doesn't improve the vent temp, I'd stop immediately since that should be more than enough to make a difference unless your A/C has other problems.
8 Otherwise, continue but stop at 500g since your system must have a at least ~200 grams to be cooling at all - the total then would be ~700 g. You don't want to increase your risk of overcharging to the point of hydrolock.

Hope this helps. Otherwise, I'm afraid it's time to go to a shop with A/C expertise.

Good luck

RDL
RDL, you are awesome I really appreciate you taking your time to try and help me out.
I got a 33PSI reading while the AC was ON and at max cool (60F reading, no MAX AC button)
Before I figured out that I had my center dash temp. thing at 2 red dots, I bought a recharge kit and recharged my AC from 32PSI to 33PSI, not much at all.
After scouring the board, I found that on the e39 with the 775g compressor, 29PSI to 32PSI is optimum range for AC functionality. But of course the PSI reading depends on things other than just the amount of R134a in the system. BTW, ALL E39 after late 1997 year changed from the original 1225g compressor to the 775g compressor, so we have the same system under our hoods.
I am kind of nervous about putting anymore R134a in my system because according sources on this board the E39 AC system is very sensitive and only handles a +/-0.5g before it starts to lose its full functionality. Sounds hard to believe, maybe it is true. So that means overcharging or undercharging will decrease the icyness of your AC.
Leaks are also a rarity on the E39 AC systems because supposedly the E39 AC systems are some of the most durable AC system out there. They were built like rocks.
But, in the end it can be like you said: these systems just don't get that cold, especially the fact that they were built in Germany, a place that sees more snow than sun. Just by putting my hand to the center vent, I would say I have anywhere from 50F to 60F airflow.
Maybe that's the best it can do, even though that is not that great at all.
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  #9  
Old 09-22-2010, 10:11 PM
GreenTiger GreenTiger is offline
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Also RDL, how do I check for a clogged evaporator. Where would I be able to reach that?
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  #10  
Old 09-23-2010, 07:34 AM
rdl rdl is online now
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Quote:
Originally Posted by King540i View Post
Also RDL, how do I check for a clogged evaporator. Where would I be able to reach that?
We must distinguish between internally, i.e. for refrigerant flow & externally, i.e. for air flow.
The evaporator is inside the HVAC air distribution box under the dash behind the center console. Roughly between the glove box and the gas pedal. Gaining access for inspection would require evacuating the refrigerant, removing much of the dash and lots of parts to get to the evaporator. A professional job or a very experienced, ambitious DIYer.

Checks possible without removal.
Internal blockage - diagnosis by A/C professional for refrigerant flow blockages

External blockage - all HVAC air follows this path
1 cabin air filters in the engine compartment (unless in recirculation mode)
2 HVAC fan/blower
3 evaporator
4 heater core
5 through duct distribution doors (footwell, dash, defrost/windshield)
6 out the vents - be sure dash vents are turned to fully open when checking those

So, if you get good air flow the evaporator is not clogged. If your air flow is poor it could be any of the components - assuming your blower fan & FSU (speed controller) are OK.
If you observe a large difference between recirculation on and off, most likely the cabin air filters are clogged.

Something else to consider. I found the following in the BMW Wiring Diagram description of HVAC operation
***********************
Temperature control
The required temperature in the passenger compartment (setpoint temperature ) is set by means of a rocker switch on the operating panel and shown in the display. The interior, heat exchanger, evaporator, outside and coolant temperatures are evaluated for the purpose of temperature control together with the driving speed and engine speed signals.

Heater operation is based on the reheat principle. The air is cooled down by the evaporator and then heated up again to the required temperature by the heat exchanger. The temperature of the heat exchanger is controlled by a clocked water valve. In this way, the control unit calculates the valve opening times dependent on the above-specified input variables. The valve opening times are 0 ms at max. COLD and 3600 ms at max. WARM.

A mechanical mixing air adjuster makes it possible to influence the outlet temperature at the ventilation nozzles. The temperature can be changed within the range from evaporator temperature to heat exchanger temperature.
***********************

If the water valves (one for each side) is/are malfunctioning you could see warm air when you're expecting cold. Or, vice versa.

I take the "ventilation nozzles" to be the dash vents. So, when you describe the red/blue wheel varying dash vent temperature, I conclude that the water valve(s) are not shutting off to zero although you have set temp to the minimum. However, the description above indicates that at 3 blue dots you should be getting the coldest air your A/C can produce.

Regards

RDL
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  #11  
Old 09-23-2010, 07:24 PM
GreenTiger GreenTiger is offline
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Quote:
Originally Posted by rdl View Post
We must distinguish between internally, i.e. for refrigerant flow & externally, i.e. for air flow.
The evaporator is inside the HVAC air distribution box under the dash behind the center console. Roughly between the glove box and the gas pedal. Gaining access for inspection would require evacuating the refrigerant, removing much of the dash and lots of parts to get to the evaporator. A professional job or a very experienced, ambitious DIYer.

Checks possible without removal.
Internal blockage - diagnosis by A/C professional for refrigerant flow blockages

External blockage - all HVAC air follows this path
1 cabin air filters in the engine compartment (unless in recirculation mode)
2 HVAC fan/blower
3 evaporator
4 heater core
5 through duct distribution doors (footwell, dash, defrost/windshield)
6 out the vents - be sure dash vents are turned to fully open when checking those

So, if you get good air flow the evaporator is not clogged. If your air flow is poor it could be any of the components - assuming your blower fan & FSU (speed controller) are OK.
If you observe a large difference between recirculation on and off, most likely the cabin air filters are clogged.

Something else to consider. I found the following in the BMW Wiring Diagram description of HVAC operation
***********************
Temperature control
The required temperature in the passenger compartment (setpoint temperature ) is set by means of a rocker switch on the operating panel and shown in the display. The interior, heat exchanger, evaporator, outside and coolant temperatures are evaluated for the purpose of temperature control together with the driving speed and engine speed signals.

Heater operation is based on the reheat principle. The air is cooled down by the evaporator and then heated up again to the required temperature by the heat exchanger. The temperature of the heat exchanger is controlled by a clocked water valve. In this way, the control unit calculates the valve opening times dependent on the above-specified input variables. The valve opening times are 0 ms at max. COLD and 3600 ms at max. WARM.

A mechanical mixing air adjuster makes it possible to influence the outlet temperature at the ventilation nozzles. The temperature can be changed within the range from evaporator temperature to heat exchanger temperature.
***********************

If the water valves (one for each side) is/are malfunctioning you could see warm air when you're expecting cold. Or, vice versa.

I take the "ventilation nozzles" to be the dash vents. So, when you describe the red/blue wheel varying dash vent temperature, I conclude that the water valve(s) are not shutting off to zero although you have set temp to the minimum. However, the description above indicates that at 3 blue dots you should be getting the coldest air your A/C can produce.

Regards
RDL
Again, thank you very much RDL

I have very good air flow on recirculation and non recirculation, so I am pretty sure that my system is not clogged. Also, my FSU is intact b/c I get different fan speeds.

During the week I am busy with school and work, so I can't really check anything during the week, only discuss and analyze previous symptoms. When the weekend comes along, I am going to check pressure again, buy a thermometer to check center dash temp. at max AC and hopefully I get some really cold air. I will probably also try adjusting R134a levels, even though I know that it is harmful to the environment and like shooting in the dark; but at least I have a range PSI I can work with.

Do you know what is the normal MAX AC temp on the E39s. Should I expect 40F at the center dash MAX AC? 50F at MAX AC?

Thanks once again RDL
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  #12  
Old 09-24-2010, 07:46 AM
rdl rdl is online now
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Quote:
Originally Posted by King540i View Post
Again, thank you very much RDL

I have very good air flow on recirculation and non recirculation, so I am pretty sure that my system is not clogged. Also, my FSU is intact b/c I get different fan speeds.

During the week I am busy with school and work, so I can't really check anything during the week, only discuss and analyze previous symptoms. When the weekend comes along, I am going to check pressure again, buy a thermometer to check center dash temp. at max AC and hopefully I get some really cold air. I will probably also try adjusting R134a levels, even though I know that it is harmful to the environment and like shooting in the dark; but at least I have a range PSI I can work with.

Do you know what is the normal MAX AC temp on the E39s. Should I expect 40F at the center dash MAX AC? 50F at MAX AC?

Thanks once again RDL
Unfortunately there will be no hard and fast answer.

The lowest vent temp will be affected several factors, independent of A/C system condition
1 ambient temp - affects the ability of the A/C to reject heat via the condenser
2 ambient relative humidity - affects the ability of the evaporator to reduce the temp of the air flow, since high humidity can use a lot of cooling capacity to evaporate water rather than reduce air temp
3 recirculation on or off - re-cooling the cool/warm cabin air will give a lower vent temp than the first pass cooling of hot outside air
4 fan speed - at lower speeds, the air is in the evaporator longer and gets colder. In my cars this effect has been 3-4F between max blower and say < 50% blower. (note though that MAX A/C and high blower speed gives more total cooling effect since the slightly smaller temp drop is more than offset by the much higher air flow volume)

All that said, the best I can do for you are these:
1 the < 59F quoted in the TIS and described in an earlier post.
With HVAC in full automatic mode, set point at 70F my car has delivered:
2 vent air 45F @ ambient 85F, 60% relative humidity
3 vent air 51F @ ambient 85F, 82% RH
The indicated blower speed was ~ 33%

Regards
RDL
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  #13  
Old 09-24-2010, 09:55 AM
GreenTiger GreenTiger is offline
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Mein Auto: 7/98 NonVanos 540iA
Quote:
Originally Posted by rdl View Post
Unfortunately there will be no hard and fast answer.

The lowest vent temp will be affected several factors, independent of A/C system condition
1 ambient temp - affects the ability of the A/C to reject heat via the condenser
2 ambient relative humidity - affects the ability of the evaporator to reduce the temp of the air flow, since high humidity can use a lot of cooling capacity to evaporate water rather than reduce air temp
3 recirculation on or off - re-cooling the cool/warm cabin air will give a lower vent temp than the first pass cooling of hot outside air
4 fan speed - at lower speeds, the air is in the evaporator longer and gets colder. In my cars this effect has been 3-4F between max blower and say < 50% blower. (note though that MAX A/C and high blower speed gives more total cooling effect since the slightly smaller temp drop is more than offset by the much higher air flow volume)

All that said, the best I can do for you are these:
1 the < 59F quoted in the TIS and described in an earlier post.
With HVAC in full automatic mode, set point at 70F my car has delivered:
2 vent air 45F @ ambient 85F, 60% relative humidity
3 vent air 51F @ ambient 85F, 82% RH
The indicated blower speed was ~ 33%

Regards
RDL
Thanks for the info. RDL

Its not very humid here in SoCal. What does TIS stand for?

What is the benefit of keeping the system at Auto mode? What does auto do?

Thanks
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  #14  
Old 09-24-2010, 01:48 PM
rdl rdl is online now
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Mein Auto: 530i 2003
TIS => technical information system (?)
A computer program/database that provides specifcations, repair instructions, special tool lists, etc. etc. Like a factory service manual.

Auto mode takes control of the HVAC fan and flappers to direct air to appropriate vents depending on whether one needs heating or cooling to reach the set point - except for the red/blue dial of course
It's described in the owner's manual.

Regards
RDL
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