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Thread: Air Conditioning Questions

  1. #1
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    Air Conditioning Questions

    1998 750iL w 70k miles - AC works, blows cold, then when the system is on for a few minutes the line that rides along the passenger (USA) fender well vibrates like crazy, then stops. AC loses cool air at vents, then repeats. No idea what could cause this, I assume pressure related. Pusher fan was running as it was supposed to.


    2001 740iL 86k miles - Today I was in park, AC on and the pusher fan was on (due to engine heat upon investigation). The car purged a pile of refrigerant, but AC still seems to be working, albeit its not hot here yet. Im just trying to understand what would cause this and/or what I should look at? Purging seems like the pressure got too high and it blew off some R134a to equalize - why is what I dont get.

    Perhaps I just need to take both in for AC service, but Id love any insight.

    Thanks!

    Here the line that vibrates wildly.

    AC LINE.jpg
    Last edited by 740ilDuke; 04-25-2018 at 09:17 PM.
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  2. #2
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    If the refrigerant was ejected then the pressure was too high - and that usually means the refrigerant temperature was excessive. As the auxiliary fan was running I would guess you have an obstruction between the radiators such as leaves. I was quite surprised when I change my evaporator just how much gets trapped in there:

    Timm..2007 E64 650i Individual Sport..1999 E31 840ci Individual Sport..ex owner of 2000 E38 740..1999 E38 740i V8 M62..1998 E38 735i V8..1993 E32 730i V8..1988 E28 518i


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  3. #3
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    Quote Originally Posted by Timm View Post
    If the refrigerant was ejected then the pressure was too high - and that usually means the refrigerant temperature was excessive. As the auxiliary fan was running I would guess you have an obstruction between the radiators such as leaves. I was quite surprised when I change my evaporator just how much gets trapped in there:

    +1 on the amount of trash that gets in there, if you find trash there check the alternator (if external) ducting.

  4. #4
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    This is my area of expertise. When the compressor is engaged the auxiliary fan should be running at slow speed.
    Timm is correct if you vented refrigerant it came out of the compressor and it would be due to high pressure. Buying and using a real set of gauges would be a big help. Based on my experience with BMW's I would put in a fan clutch before anything else, after cleaning the leafs out of course. When you start the car you should here the engine fan and after a few minutes it will get quiet. There is a pressure switch on the Accumulator/Dryer. That switch controls the auxiliary fan speed and the compressor cut out. based on the fact that the compressor did not cut out you either have a plugged condenser or the switch does not work. another possibility is that the system was over charged.

    As for the other car I would guess that the expansion valve has failed or is plugged. You would get some initial cooling but as soon as the pressure goes high enough the compressor will cut out on high pressure. You can see the clutch if you look down on the passenger side front of the engine. It should start and stop when running normally. The best place to test your system is parked with the AC on and the controls set to recirc with full heat. The system works the hardest when there is no air from driving.

    To all that read this, DO NOT PUT ANY SNAKE OIL OR LEAK SEALERS IN YOUR SYSTEM! they may work but if they don't you will ruin your whole system. All that belongs in the AC system is the proper refrigerant and the proper oil in the correct amounts. The refrigerant carries the oil so if you don't put in the correct oil you will be buying a compressor. If you put in a new compressor do not flush the system put in the inline filter in the photo in the liquid line before the expansion valve.
    Attachment 627821
    Last edited by acspecialists; 04-25-2018 at 10:45 AM. Reason: add photo

  5. #5
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    Great info!

    2001 740iL -
    From a cold start the belt driven fan is spinning, seems to be doing its job. Clutch feels like it has the usual amount of drag when spun by hand. The pusher did not cut on with the AC on max and it purged again. So, im trying to decide on buying a pusher fan or what at this point. This is the daily driver, so im tabling the 750 AC issue for now.



    Quote Originally Posted by acspecialists View Post
    This is my area of expertise. When the compressor is engaged the auxiliary fan should be running at slow speed.
    Timm is correct if you vented refrigerant it came out of the compressor and it would be due to high pressure. Buying and using a real set of gauges would be a big help. Based on my experience with BMW's I would put in a fan clutch before anything else, after cleaning the leafs out of course. When you start the car you should here the engine fan and after a few minutes it will get quiet. There is a pressure switch on the Accumulator/Dryer. That switch controls the auxiliary fan speed and the compressor cut out. based on the fact that the compressor did not cut out you either have a plugged condenser or the switch does not work. another possibility is that the system was over charged.

    As for the other car I would guess that the expansion valve has failed or is plugged. You would get some initial cooling but as soon as the pressure goes high enough the compressor will cut out on high pressure. You can see the clutch if you look down on the passenger side front of the engine. It should start and stop when running normally. The best place to test your system is parked with the AC on and the controls set to recirc with full heat. The system works the hardest when there is no air from driving.

    To all that read this, DO NOT PUT ANY SNAKE OIL OR LEAK SEALERS IN YOUR SYSTEM! they may work but if they don't you will ruin your whole system. All that belongs in the AC system is the proper refrigerant and the proper oil in the correct amounts. The refrigerant carries the oil so if you don't put in the correct oil you will be buying a compressor. If you put in a new compressor do not flush the system put in the inline filter in the photo in the liquid line before the expansion valve.
    Attachment 627821
    2001 | DINAN 7 Sport | S62 Swapped 6-Speed
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  6. #6
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    The pusher fan cuts on when the engine temp gets hot, but not when the AC is ON.
    Last edited by 740ilDuke; 04-25-2018 at 09:32 PM.
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  7. #7
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    Quote Originally Posted by acspecialists View Post
    There is a pressure switch on the Accumulator/Dryer. That switch controls the auxiliary fan speed and the compressor cut out. based on the fact that the compressor did not cut out you either have a plugged condenser or the switch does not work.
    Is that sensor located underneath the air box, behind passenger headlamp? I think PN#64539323658 https://www.ecstuning.com/b-acm-part...539181464~acm/

    Replacing this might be the best first option, refilling and seeing if the pusher works. Im curious if pusher fan could be functional, but only for the engine heat sensor? No debris in the radiator/evaporator area. The pusher didn't cut on today when testing with AC on. The fan did cut on from engine heat, AC OFF after driving and sitting in park at idle.
    Last edited by 740ilDuke; 04-25-2018 at 09:38 PM.
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  8. #8
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    As the system is venting and the pusher fan is not running I would suspect the high pressure switch. If you can dig up a pin out you could test the system by jumping out the leads.

    When the pusher fan came on were there two speeds?

  9. #9
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    Is that part above the pressure switch - or is that something else?

    Im not positive if the pusher ran two speeds. It did the clockwise bump to the right twice, then took off.


    Quote Originally Posted by acspecialists View Post
    As the system is venting and the pusher fan is not running I would suspect the high pressure switch. If you can dig up a pin out you could test the system by jumping out the leads.

    When the pusher fan came on were there two speeds?
    2001 | DINAN 7 Sport | S62 Swapped 6-Speed
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    Dual Pane Glass | Black & Sand Int.

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  10. #10
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    Since this thread has collected the AC guys attention, I'll post my question here instead of starting a new thread. Hope you don't mind a tiny hijack Duke!

    I have a wild vibrating line too, and I think whatever it is causing the vibration is giving me a good shake all around at idle. I only really notice it at idle. My line is on the drivers side. It was bad enough when it started (I bought the car while it was cold outside, so it started when I begun needing the AC) that I pulled over to check out what was going on. Here is the hose that was going crazy in mine:

    20180406_115803.jpg

    It's that line that has the loom on it in the center of the picture. It was up against that hard line you see, and that hard line had eaten through the loom and started on the hose itself. I noticed there was a "bracket" on the hose that was supposed to be holding it... somewhere, somehow. I didn't know where it was SUPPOSED to mount, it's just a silver wire bracket thingie. I propped it against something on the fender side, and that now keeps it off the hard line and keeps the noise down. I'm not sure that hose is even AC related. I kind of think its transmission related. But it only does it's crazy shake thing when the tranny is in gear and the AC is on. It will not go crazy in Park or neutral with AC on. It will also not go crazy in gear with the AC off. Here a pic of how I rigged it up, I'd love to know where that silver bracket is SUPPOSED to mount, once again it's the hose in the center of pic with loom on it:

    20180407_153143.jpg

    But either way, it still vibrates like crazy with the AC on, it's just more controlled and less intense inside the car with it moved off the hard line and the inner wheel well. I don't really think it's supposed to be going crazy like that.

    Anyway, any ideas?
    Last edited by 951Dreams; 04-26-2018 at 04:10 AM.
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  11. #11
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    Quote Originally Posted by 740ilDuke View Post
    The pusher fan cuts on when the engine temp gets hot, but not when the AC is ON.
    The auxiliary fan should not be cutting in at idle unless you are not getting enough air through the radiators - which again points to debris between the radiators or a failing viscous-coupled fan....
    Timm..2007 E64 650i Individual Sport..1999 E31 840ci Individual Sport..ex owner of 2000 E38 740..1999 E38 740i V8 M62..1998 E38 735i V8..1993 E32 730i V8..1988 E28 518i


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  12. #12
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    I believe the pusher fan on the '01 740IL is controlled by the climate control module and looks at coolant temperature, refrigerant pressure, speed and some other inputs then decides what percentage to run the fan. Also be reminded to force open the A/C outside air vents (under the hood) if you have the hood open while trouble shooting.

  13. #13
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    Quote Originally Posted by 951Dreams View Post
    Since this thread has collected the AC guys attention, I'll post my question here instead of starting a new thread. Hope you don't mind a tiny hijack Duke!

    I have a wild vibrating line too, and I think whatever it is causing the vibration is giving me a good shake all around at idle. I only really notice it at idle. My line is on the drivers side. It was bad enough when it started (I bought the car while it was cold outside, so it started when I begun needing the AC) that I pulled over to check out what was going on. Here is the hose that was going crazy in mine:

    20180406_115803.jpg

    It's that line that has the loom on it in the center of the picture. It was up against that hard line you see, and that hard line had eaten through the loom and started on the hose itself. I noticed there was a "bracket" on the hose that was supposed to be holding it... somewhere, somehow. I didn't know where it was SUPPOSED to mount, it's just a silver wire bracket thingie. I propped it against something on the fender side, and that now keeps it off the hard line and keeps the noise down. I'm not sure that hose is even AC related. I kind of think its transmission related. But it only does it's crazy shake thing when the tranny is in gear and the AC is on. It will not go crazy in Park or neutral with AC on. It will also not go crazy in gear with the AC off. Here a pic of how I rigged it up, I'd love to know where that silver bracket is SUPPOSED to mount, once again it's the hose in the center of pic with loom on it:

    20180407_153143.jpg

    But either way, it still vibrates like crazy with the AC on, it's just more controlled and less intense inside the car with it moved off the hard line and the inner wheel well. I don't really think it's supposed to be going crazy like that.

    Anyway, any ideas?
    That is the power steering line from the pump to the steering box, it is completely unrelated to the AC system.

  14. #14
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    +1, I think when the AC is on the engine speed changes and causes the vibration.

    I'll have to check unless someone weighs in but I believe that all of the signals go to the climate control module as inputs. Then based on conditions it sends the necessary outputs to the equipment. Its a pain in the neck. All you need is a fan clutch, high and low pressure switches and an onoff button.

    I believe I remember a thread where I guy switched out the controls and lost the Aux fan.

  15. #15
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    On the passenger side of the engine you will find the discharge line from the compressor. The liquid line from the condenser to the Filter/dryer. From the filter/dryer is the liquid line to the expansion valve inside the air box just before the evaporator. Without gauges you can feel the lines and figure thinks out. Before you start make sure the AC is on and the clutch is engaged. Set the temp for 85 and open the recirc, turn the fan on high, shut all of the windows and doors, this will be your heat load.

    As the system runs the engine fan should start to engage when the heat load rises. The pusher fan is run with PWM so it should come on and start to speed up as the heat load rises. You can touch the discharge line and it should be hot, in my case warm because its a cool morning and I know mine is working fine. If you have a temp gun you can shoot it, for R134a the temperature pressure relationship is nearly identical. If you are getting 200deg thats about 200psi. The outlet from the condenser should be significantly lower, if it is not there is a problem with the condenser or the fans.

    Next up is the filter/dryer under the air box. It has no sight glass so no cheating on the charge. It does have a pressure switch with three wires. Just guessing but one would be the common, one for the fan and one for the cutout. If the compressor is running you can unplug the switch and the compressor should clutch out. BMW did not include a schrader valve so you will have to recover the system to change the switch out.

    From there the liquid goes to the expansion valve then the evaporator. The line coming back from the firewall to the compressor is the low side return to the compressor. If you have enough refrigerant it should be cold and condensing water. And then the process starts all over again. The purpose of the AC system is to remove water not control temperature. It should always be left on.

    A couple more things to look for. If the system has a restriction you will find a frosty spot where the restriction is. For example your Filter/Dryer gets frosty, its plugged. Looking for leaks, when the refrigerant leaks it carries oil with it. You will find a dirty oily spot where the leak is. BMW used the best type of fitting so leaks are rare. Look at the front of the clutch if its oily and dirty that's your leak. A set of gauges will make a big difference in TS.

  16. #16
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    The radiators are clean as a pin, I always spray them heavily when i wash the car.

    When I unplugged the pressure switch the clutch on the compressor does not cut off.

    I have had the AC panel disconnected when I was installing the NBT, but its not a different panel
    so I cant imagine it made any difference. All buttons work, MAX A/C etc.

    Im tempted to buy a new fan clutch, electric fan and pressure switch.

    With the engine at idle, AC on and at operating temp, I can easily stop the engine fan with my hand. So maybe I should start with
    that swap, and go forward. It's purged twice now, so I know it will need a top off of R134a. It blows cold air once the engine heat
    forces the pusher fan to turn on.

    Quote Originally Posted by Timm View Post
    The auxiliary fan should not be cutting in at idle unless you are not getting enough air through the radiators - which again points to debris between the radiators or a failing viscous-coupled fan....
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  17. #17
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    The pressure switch is #1, it controls the pusher and the high cut out. I guess you would have to make sure there isn't a fuse the the circuit. That will solve the venting but the real problem is "what is causing the high pressure". If no fans are working that should be the smoking gun.

  18. #18
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    I replaced the viscous clutch today, definitely moving more air. Mine was moving air, but not as much as the new one. 17 years of spinning, it was time to go anyway.

    75 degrees outside, AC on 85 w/ recirc on it idled for 20-25 minutes and got down to 97c on the cluster. It is actually cooling pretty well to be low on refrigerant, but I'll replace that sensor when it arrives and have it topped off. Hopefully the clutch was the culprit, I'm sure my cooling system will be happier with the air moving around a bit more.

    Now to figure out the 750 and it's vibrating AC line issue. Could the pressure switch cause that to happen, or am I barking up the wrong tree for that issue?

    - - - Updated - - -

    Replaced the viscous clutch today, seems happier - but havent refilled it with r134a yet.

    Thank you, all - I think I'll have a cool summer.

    Quote Originally Posted by Timm View Post
    The auxiliary fan should not be cutting in at idle unless you are not getting enough air through the radiators - which again points to debris between the radiators or a failing viscous-coupled fan....
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  19. #19
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    Sounds like you nailed it. Here's a few more tips,

    After you recover the refrigerant and change the switch you must evacuate the system. This is the most important and overlooked procedure when it comes to AC service. The evacuation pumps out all of the air(oxygen and nitrogen) and at 30in of vacuum flashes and moisture and pumps it out. This should be done for 45min. Then you will have your first chance at a leak test, you should lose no more that 5" of vacuum in 5min.

    If you charge from a 30# bottle you can now suck in the proper amount through the high side as a liquid. Do not charge the low side with liquid you will sulg the compressor and destroy it. If you are charging from a 12oz can warm it up and hold the can upright. When the can is empty it will warm back up after freezing.

    Finally to check you system without gauges set the climate control to normal settings and after 20-30min see if the low side return starts you condense moisture? If you do condense moisture the refrigerant cycle is complete even if the system may not have every ounce that is required.

  20. #20
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    Thanks! Ill add this to my notes. I'll be taking it to a shop for the refill so they can pull a vacuum on it. With summer on approach, I need that to work flawlessly.


    Quote Originally Posted by acspecialists View Post
    Sounds like you nailed it. Here's a few more tips,

    After you recover the refrigerant and change the switch you must evacuate the system. This is the most important and overlooked procedure when it comes to AC service. The evacuation pumps out all of the air(oxygen and nitrogen) and at 30in of vacuum flashes and moisture and pumps it out. This should be done for 45min. Then you will have your first chance at a leak test, you should lose no more that 5" of vacuum in 5min.

    If you charge from a 30# bottle you can now suck in the proper amount through the high side as a liquid. Do not charge the low side with liquid you will sulg the compressor and destroy it. If you are charging from a 12oz can warm it up and hold the can upright. When the can is empty it will warm back up after freezing.

    Finally to check you system without gauges set the climate control to normal settings and after 20-30min see if the low side return starts you condense moisture? If you do condense moisture the refrigerant cycle is complete even if the system may not have every ounce that is required.
    2001 | DINAN 7 Sport | S62 Swapped 6-Speed
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