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Thread: Cold Rear, Warm Front AC - I may have disovered the Fix with the Regulator!

  1. #1
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    Cold Rear, Warm Front AC - I may have disovered the Fix with the Regulator!

    The "Voltage Regulator", a non-electronic device that sits on the passenger/compressor side of the engine compartment is the "unknown" in our HVAC systems, apparently balancing front and rear units. Over the years many have suggested that a low charge is to blame. Next its the dreaded and difficult to source "front" expansion valve which requires complete disassembly of the center console. I've just done my second replacement of the front and rear valves and have always been plagued with warm air from the front vents. In the process of reassembling the system following flushing all lines, replacing my compressor (which has a clogged screen on the return/suction side) with a Sanden 508 and knowing that this regulator is still available, I decided to take it apart and inspect its inner workings. After removing the spring and diaphragm I attempted to remove the valve/piston and it wouldn't budge, needing to replace the screw and then use pliers to pull it out. It was dirty and as a result it was stuck. 29 years old, grime/contaminants had logged between the piston and the wall, likely keeping it from "regulating" pressure. You'll see the recessed portion of the piston. If there is excess pressure in the system it will vent it through the small tube that comes off the top of the regulator and connects to the front expansion valve. picture below is after all was cleaned, the recessed area was filthy, nearly black, in part contributing (I'm sure) to high pressure readings on my gauge whenever we checked the system. In flushing the system and then blowing out with compressed air I learned that similar to holding your finger over the outlet you are flushing, you build up pressure and draw more moisture and contaminants through the small vented opening you have created. This seems to be the same principal as to why expansion valves get clogged so easily and why an ultra clean system is imperative to good system performance. Will keep all posted but do believe that I have found the silver bullet to ice cold air from the front vents, perhaps an easier fix (at least first step) than the presumed "front" expansion valve that requires tearing the dash apart. I do hope that I am right. Have a look at the pics. Dirty Q tips are all from the valve body.

    Further, here's a great link from a board on ACsource.net with individuals trying to figure out this valve over the years:

    http://acsource.net/acforum/viewtopic.php?f=1&t=4378
    Attached Images Attached Images
    Last edited by jeffcfp1; 08-25-2017 at 07:17 PM. Reason: Additional Info

  2. #2
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    What is the Part #?
    Jay
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  3. #3
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    Quote Originally Posted by master6 View Post
    What is the Part #?
    The p/n is 64511380659.

    Hopefully the fix mentioned above will solve the problem. I've been having the same issue.

  4. #4
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    I'd also like to add some info concerning the science of evaporator valves, particularly concerning the "sensing bulb", the bullet looking part of the valve that senses "superheat". I believe this link also mentions heat conductive paste, i.e. the goo that surrounds the bulb. Fortunately, I still have access to remount the bulb, (mine was clipped to both lines versus just the return - may have also contributed to the valve not opening enough to let refrigerant into the front evaporator!

    http://www.achrnews.com/articles/850...pansion-valves

    - - - Updated - - -

    Hakeem, in the long thread you mentioned a leak in the diaphragm and that you sealed it. Did you notice if your valve was frozen as well? Again, I had to use force to remove the piston. When held vertically it now moves in either direction on its own from gravity, i.e. before hooking up the spring.

  5. #5
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    Ok, let's put our collective heads together and try to make sense of it all in a simpler picture. We are focused on the front part of the system, so I will not worry about detailing the rear, because it seems to keep on working just fine in all cases. The quick drawing below shows what I think is going on in the system.
    bmw635acdiagram.JPG

    Let's keep in mind that the expansion valves are pre-set to allow gas through at only a certain pressure. What I believe happens is as follows.

    1.) The compressor starts running, and pressure in the entire system goes up.
    2.) The expansion valves allow flow when high pressure exceeds a given point, but the front valve requires back pressure to open.
    3.) The regulator on the low pressure line has an adjustable set-point. When the low side pressure reaches the desired point, the regulator sends pressure to the forward expansion valve.
    4.) The gas pressure to the forward valve opens it.
    5.) The capillary sensor mounted on the exchanger gets cool when it is working. If the fluid in the capillary gets too cold, there is a "spacer" inside the valve that shrinks, and cuts off regulator feed pressure.

    So in operation...
    1.) Everything is fine when the compressor high pressure, and regulator feed pressure to the front expansion valve are normal.
    2.) When regulator feed pressure cuts off, the valve closes.
    3.) When the capillary gets too cold and the fluid shrinks, the valve closes.

    Remember that the exchanger operates by getting a low pressure/flow of liquid and letting it expand, what all of the above means is that in normal operation, the valve cycles open closed regularly. Depending upon the pressure getting to it from the regulator and the capillary heating/cooling the valve keeps on feeding liquid refrigerant to the exchanger.

    Assuming the understanding above is correct, let's lets reason our way through what could cause some problems.

    1.) Low refrigerant means overall lower pressures on both high and low sides of the circuit. If the low side pressure doesn't get high enough, the forward valve can't operate due to lack of back pressure. So the rear AC will keep running, but the front won't if refrigerant levels are low.

    2.) A faulty capillary will prevent the valve from opening under all conditions, so you would have to replace it altogether if a.) the front never cools at all, b.) if pressures are same on both high/low sides, or c.) if the exchanger is constantly icing over.

    3.) If the high/low pressure differential seems ok, but the front doesn't cool, then it could be a bad expansion valve that is not opening at all, or it could be a lack of flow from the regulator to the back-pressure sensing part of the valve.


    Again we can say that if all the above is correct, JeffCP1 has helped us to better understand the system. The regulator makes sure that both the front and rear expansion valves get the right amount of refrigerant flow for ideal function. If the rear is cold, but the front is not, then we should be able to adjust the regulator and get both units to have the same output.

    Jeff's observations about his regulator also make a ton of sense. If the piston is binding, then no amount of adjusting will help, because the pressure can't cycle to the front valve. The spring just compresses, but the valve doesn't move. I need to get the system evacuated and take apart that reg. I bet you mine is all gummed up too.

    Jose
    Last edited by DaHose; 08-27-2017 at 12:15 AM.
    1987 M6
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  6. #6
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    Jose, thanks for posting and for the great drawing. Below all will see a dissected expansion valve, similar to the front expansion valve on dual systems, which have the bypass feed that is feed by the regulator up on the fender well/return before the compressor. Further reading this a.m. confirms info from the acsource link in my original post at top of thread as the "blow off" regulator valve is designed (and placed shortly before the compressor/suction port) to PROTECT the compressor from excess pressure. Per the video below, this ultra small tube that feeds the front expansion valve and sends modulating/contra pressure against the underside of the diaphragm controlled by the bulb, i.e. the CO2 filled bullet looking sensor. Seems pretty clear to me that when the regulator valve is open (due to excess pressure), this extra pressure keeps the front expansion valve from fully opening - again, see link below. The system is our cars is just that, a system. If part of the system is not functioning it will offset/effect something else. AC systems function based on pressure. If my original hypothesis holds (and video below seems to support it) excess pressure (which is typically from system blockage) is keeping the front expansion valve from opening - so perhaps not so much a low charge as has always been the consensus on these boards over the years. I also saw on a youtube from Vintage air on the Sanden compressor that liquid will damage the compressor. Just a further hypothesis but further connecting the dots, my compressor seemed to have overheated due to a lack of oil. Determined this when tried to drain it, nothing came out! What happened? Maybe the regulator failed (it was frozen) and liquid refrigerant purged it of its oil.

    So, back to my original post, seems a dual system repair/troubleshooting for dash vents being warm should begin with evacuating the system and then inspecting the most easily accessible part of the dual system setup - the regulator.
    https://www.youtube.com/watch?v=yDmpKYWXai0#t=352.49621
    Last edited by jeffcfp1; 08-27-2017 at 07:33 AM.

  7. #7
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    Still have some work to do as I'm not at temperature I believe I should be at, (going to evacuate and recharge with exact 3.68 lbs of refrigerant and try to determine if I used too much oil) front and rear are the exact same temperatures, 49 degrees. So, having done front and rear expansion valves years ago and still had air from front vents warm, as I previously posted, my gummed up and frozen front regulator was apparently the culprit.

  8. #8
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    Evacuated system and recharged with dial guage at 3.6lbs on old White Industries R-12 machine I stole for $200 off of Craigslist. Front ducts 40, rear just under 40. Mystery of "warm air from front vents" solved. A summary of what I did:
    Replaced front and rear expansion valves (however, both appeared fairly clean and likely were functioning).
    As noted above, removed front "Voltage Regular", disassembled and thoroughly cleaned, this was apparently the Achilles heel - it was seized/i.e. gummed up after 30 years. THIS valve should be removed and disassembled prior to going through the painstaking process of removed front expansion valve!
    Replaced the stock compressor with a Sanden 508. Used adaptor brackets from seller on mye28. Note: Mounted the compressor with ports facing 9 o'clock versus 12 to clear euro headers on S38 motor.
    Flushed all lines, expansion valve and condenser clean, used 12" pipe cleaners to clean as well.
    Didn't replace condenser and doesn't seem to be a need to unless you are switching to/running R134.
    Replaced shorted auxiliary/pusher fan with 16" Spal fan.
    Repaired flapper doors above evaporator, mine were stuck open. I used Dremel to slice flap enough to force a new hinge into it, using tip of a finish nail to replace broken plastic hinge (epoxied into slot)

  9. #9
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    Quote Originally Posted by jeffcfp1 View Post
    I'd also like to add some info concerning the science of evaporator valves, particularly concerning the "sensing bulb", the bullet looking part of the valve that senses "superheat". I believe this link also mentions heat conductive paste, i.e. the goo that surrounds the bulb. Fortunately, I still have access to remount the bulb, (mine was clipped to both lines versus just the return - may have also contributed to the valve not opening enough to let refrigerant into the front evaporator!

    http://www.achrnews.com/articles/850...pansion-valves

    - - - Updated - - -

    Hakeem, in the long thread you mentioned a leak in the diaphragm and that you sealed it. Did you notice if your valve was frozen as well? Again, I had to use force to remove the piston. When held vertically it now moves in either direction on its own from gravity, i.e. before hooking up the spring.
    Kind of late to seeing this. Thanks for the follow up. Mine had a rip and I glued the diaphragm and was quite stuff so I'm guessing that's been my issue. Having been working on mine for years sometimes I wish I had an earlier e24 without the rear AC to avoid all the mysteries included with servicing the later ones.

    Also what do you mean by "mine was clipped to both lines versus just the return?" How did you mount your bulb? Mine isn't OEM so my replacement has a longer wire if I recall correctly, so I've been unsure exactly how to mount it.

  10. #10
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    Hakeem, mine is mounted outside of evaporator box just before the line turns towards the firewall on the larger (low pressure) return line. Here is specific industry practice for mounting: The sensing bulb should be attached at 12 o’clock on any suction line of 7/8-inch diameter or smaller. On lines larger than 7/8-inch diameter, the bulb should be placed at either 4 or 8 o’clock. The bulb should never be placed at 6 o’clock.
    Always insulate the entire sensing bulb after installation.
    Pretty simple but if as novices, we don't know that the bulb is the controller of superheat which opens and closes the front expansion valve, the valve may not be opening sufficiently.
    As a f/u to my bit of research on the role that the regulator on the fender plays, watch this video. This guy, greyfurnaceman.com can teach us all a real lot. https://www.youtube.com/watch?v=yDmp...mllAC1f22MWcQ7 Skip to 1:30ish and you'll see the cutaway showing what the small relief line from the regulator does in influencing the opening of the front expansion valve. Again, the piston in my "voltage regulator" wasn't functioning.

  11. #11
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    Quote Originally Posted by jeffcfp1 View Post
    Hakeem, mine is mounted outside of evaporator box just before the line turns towards the firewall on the larger (low pressure) return line. Here is specific industry practice for mounting: The sensing bulb should be attached at 12 o’clock on any suction line of 7/8-inch diameter or smaller. On lines larger than 7/8-inch diameter, the bulb should be placed at either 4 or 8 o’clock. The bulb should never be placed at 6 o’clock.
    Always insulate the entire sensing bulb after installation.
    Pretty simple but if as novices, we don't know that the bulb is the controller of superheat which opens and closes the front expansion valve, the valve may not be opening sufficiently.
    As a f/u to my bit of research on the role that the regulator on the fender plays, watch this video. This guy, greyfurnaceman.com can teach us all a real lot. https://www.youtube.com/watch?v=yDmp...mllAC1f22MWcQ7 Skip to 1:30ish and you'll see the cutaway showing what the small relief line from the regulator does in influencing the opening of the front expansion valve. Again, the piston in my "voltage regulator" wasn't functioning.
    2A2D9D8B-E14A-487F-973A-1EA38CC719A9.jpgB71C5B0C-57BC-43FD-A545-7AB5360158BB.jpg

    Appreciate your thread. Mine was gummed up and was ripped all around. You can also see around the diaphragm is wet so there’s definitely a leak. I assume all my problems i had were caused by this. I’ll have to try sourcing a new one.

  12. #12
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    Yes, definitely a leak as that side should be dry. Have you removed the piston? Did it move freely? As posted, I had to put the screw back in the top and put pliers on it to pull it out.

  13. #13
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    Quote Originally Posted by jeffcfp1 View Post
    Yes, definitely a leak as that side should be dry. Have you removed the piston? Did it move freely? As posted, I had to put the screw back in the top and put pliers on it to pull it out.
    I did get my piston out. It was stuck and I had to use force to get it out. This is weird since this is a brand new regulator. I'm guessing it must've gotten damaged when others decided to test for leak using pressurized air, either that or I got a bad one. I also wonder where green stuff came from since the refrigerant added was colorless and not green.
    Last edited by hakeem43020; 09-25-2017 at 11:11 PM.

  14. #14
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    Interesting. Can you post pics of the piston? Curious if the recessed area that feeds the tube that runs to the front TXV was all black and cruded as my 30 yo one was. Did you have a compressor failure? Perhaps system suffered from a lack of oil at some point - but doesn't explain the green sh*t on the other side of it.

  15. #15
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    Quote Originally Posted by jeffcfp1 View Post
    Interesting. Can you post pics of the piston? Curious if the recessed area that feeds the tube that runs to the front TXV was all black and cruded as my 30 yo one was. Did you have a compressor failure? Perhaps system suffered from a lack of oil at some point - but doesn't explain the green sh*t on the other side of it.
    1ADA39EC-15D6-41D8-BDE3-196B4B2F69B8.jpg
    Sure thing. Mine was still in good condition. It was only the diaphragm. My old piston was also in the same condition but The low side charging port broke off my original so I had to replace it with this one. I regret throwing the whole thing away because I could’ve reused the diaphragm since it wasn’t leaking. Not sure if I should be worried about the green stuff or not.

    213C4910-2416-4AAD-ACB6-F4BB967ED99B.jpeg
    Also found my bulb basically dangling after pulling my insulation off. Not sure if I missed it but did you attach your bulb to the straight section or to the angle section of the pipe where it goes to the firewall?
    Attached Images Attached Images
    Last edited by hakeem43020; 09-26-2017 at 05:15 PM.

  16. #16
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    I think bulb questioned answered on the other thread - just before the bend so that body has full contact with high pressure line. Clamp it just to the high pressure line and again, if using a screw type clamp position on underside on pipe so its out of the way of ever removing the transistor.

  17. #17
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    Quote Originally Posted by jeffcfp1 View Post
    I think bulb questioned answered on the other thread - just before the bend so that body has full contact with high pressure line. Clamp it just to the high pressure line and again, if using a screw type clamp position on underside on pipe so its out of the way of ever removing the transistor.
    Thanks. I think you solved all the problems I've been having.

  18. #18
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    Eager to hear how you make out. Today's temperatures were below 70, both front and rear gauges were sub 40, you'll be a happy, cool camper when you are done.

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