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Thread: A/C feels mildly cold even after service

  1. #1
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    A/C feels mildly cold even after service

    Hey guys, been going at this A/C issue for quite some time. Some background: Had original R12 system, completely empty. Replaced Receiver/dryer, swapped fittings, vacuumed and filled. A/C was blistering cold even while stopped. Mind you, this was done with a cheap vacuum pump and some horrid excuse for a manifold gauge. The AUX fan at this point was inoperative at low speed due to a bad resistor. System then leaked out within 3 days, found a leak in the sightglass. Tightened down, no more leaks.

    I then went ahead and recharged the system again myself without vacuuming anything. A/C was very cold, just as before. A few weeks later I went ahead and replaced the failed resistor on the AUX fan, fan works now as soon as the A/C is turned on and stays on. After this a few days later I noticed weak A/C. It was not nearly as cold, and at times would feel like it was just blowing ambient air, then cold then ambient etc.. Took it to the A/C shop to have the system evacuated and recharged, $150 later same thing. Was recharged with the correct amount for R134 3.5lbs.

    They checked the system pressures and said all looks perfect. Not sure what could be going on. Compressor clicks on and off within 20 or so seconds on each cycle. Could this point to a failing expansion valve? Surely a failing expansion valve would show up as a bad pressure reading on the high or low side correct?



    Sergio S.

    BMW 7er Website www.7er.com
    1989 BMW 735i Schwarz (sadly, sold) // 1989 BMW 750iL Cirrusblau Metallic // 1998 BMW 740iL Oxfordgrün Metallic // 2000 M5 Carbon Schwarz ///

  2. #2
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    Only thing I can think of Serge is your evaporator. If you changed over to R134a and never changed the evaporator you might still have the one with the copper core. 134 and copper core evaporators do not do well together. You might want to change out the evaporator to an all aluminum one. REIN makes one for about 115.00 with the new expansion valve attached from the factory. Peter just installed that for me along with a new BEHR correct 134 condenser. Everything is back to ice cold now. Parts are really cheap considering what they were 10 or 15 years ago. I paid less than 325 bucks for the Evap, Conden, dryer, control switch and evap temp sensor. Nice neat package and about 1/3 the price of what it was back in the mid 2000's when I did this before.

    This is what came with the car

    This is the Aluminum one
    Last edited by CroughtonE32; 10-19-2018 at 09:22 PM.
    1990 735I (Auto) E32 Feb 1990 to Present
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    1983 733I (5 Speed) E23 April 1983 to Feb 1990
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  3. #3
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    Check once more the filling. I had that this summer too. Used the simple connector with pressure gauge from these refilling kits, found out the filling was close to low, but still on normal range, filled 1 small can more and it was nice cold again, gauge was now closer to red = overfill, but still in normal pressure range, so the normal range from low to high indication makes a big difference.
    Also remove next to the e-box the black plastic cover held by 2 large plastic nuts, below that you can see the sight glass http://www.meeknet.co.uk/E38/AC/Index.htm
    If your system is operating but short on gas you should see bubbles going past. Here there are differences between R12 and R134a, master CroughtonE32 will explain in detail, we just discussed that by PM.
    Last edited by shogun; 10-19-2018 at 10:56 PM.
    Shogun tricks and tips for the E32 series are HERE!

  4. #4
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    Quote Originally Posted by CroughtonE32 View Post
    Only thing I can think of Serge is your evaporator. If you changed over to R134a and never changed the evaporator you might still have the one with the copper core. 134 and copper core evaporators do not do well together. You might want to change out the evaporator to an all aluminum one. REIN makes one for about 115.00 with the new expansion valve attached from the factory. Peter just installed that for me along with a new BEHR correct 134 condenser. Everything is back to ice cold now. Parts are really cheap considering what they were 10 or 15 years ago. I paid less than 325 bucks for the Evap, Conden, dryer, control switch and evap temp sensor. Nice neat package and about 1/3 the price of what it was back in the mid 2000's when I did this before.

    This is what came with the car

    This is the Aluminum one

    What kind of symptoms does using a copper core with 134 create? Im sure it has never been changed, but my previous 735i also had the original core with freezing cold A/C. How much did Peter charge you to install it? I cant imagine the amount of work required to do this unless the unit can be slid out from the expansion valve side without needing to remove the dash.

    Quote Originally Posted by shogun View Post
    Check once more the filling. I had that this summer too. Used the simple connector with pressure gauge from these refilling kits, found out the filling was close to low, but still on normal range, filled 1 small can more and it was nice cold again, gauge was now closer to red = overfill, but still in normal pressure range, so the normal range from low to high indication makes a big difference.
    Also remove next to the e-box the black plastic cover held by 2 large plastic nuts, below that you can see the sight glass http://www.meeknet.co.uk/E38/AC/Index.htm
    If your system is operating but short on gas you should see bubbles going past. Here there are differences between R12 and R134a, master CroughtonE32 will explain in detail, we just discussed that by PM.
    I will have to check it to see what my cheap one says. When I had it done by the shop, they used a machine specific to that, digital and added 3.5lbs of 134. I will check the sight glass again, but last time I never saw any bubbles going past it. I also want to add something. When running the A/C, in these old E32s I was used to hearing the gas "hiss" behind the dash when the A/C was on, on my car now, it will make a "hiss" sound for about half a second, cool for a little, then stop cooling. Its honestly acting as if its out of gas.

    BMW 7er Website www.7er.com
    1989 BMW 735i Schwarz (sadly, sold) // 1989 BMW 750iL Cirrusblau Metallic // 1998 BMW 740iL Oxfordgrün Metallic // 2000 M5 Carbon Schwarz ///

  5. #5
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    On my E32 M30 to get the evaporator out, you remove the glove box, you loosen up both A/C pipes on the passenger side under the hood so things can move, then the side panel and just about what you do to replace the SWORD. Then the evaporator slides out on the passenger side. I saw it once done many years ago, this time I wasn't at the shop when Peter did the work. I'm not sure of the price because we did a lot more than just that. I never have him itemize. He just gives me a price for everything and I'm always amazed at how generous he is with his time. I just PM'd with the master here and I'm going to copy and paste what I asked him and what he said.

    Hi Erich, I didn't post this but I wanted to just run it by you. I heard from a guy at Vista BMW who is one of the older mechanics last month. I had to go to the rear where the wholesale parts are sold to pick something up for a shop friend. I was talking to the mechanic about that sight glass and the bubbles I see there even when my system is full and ice cold. He said that the 134 refrigerant can not be thought of like the R12 when it comes to using the sight glass to know that the system is free of air and filled. Never mentioned this to anybody, but I wonder if you've heard this at all. It was just a conversation with one of the older guys who has been there for years and works on our cars.
    Jeff


    He is exactly right. I did not know that too when I had my trouble, only thought about bubbles, looked at the tester, confused. Then I called my buddy, he said with R134a you always still see some bubbles. But when it was on the lower side of normal, I could see larger bubbles and when I filled up R134a, these bubbles were much smaller accdg to my impression (similar to maybe gas in a sparking water bottle), but they were still there. Good point here. Better you mention that in that thread because not many people know that. You can tell them what the older mechanic said that and my own experience this summer. Apparently with R134a there are always some bubbles and maybe ... only the experts can see the difference in the sight glass. So I thought at that moment, use the sight glass plus the test gauge and then find out what fits. After I filled the 1 gas can, I left the empty can +the gauge there and let the engine run and could see the changes in pressure when compressor was on an off cycling, some people do the test too short and just have the result of a cycle.

    In answer to your other question about the copper original evaporator, all I can say is that all the mechanics were amazed to see how eaten up it was when pulled out to be replaced. They spoke to one of the service managers at Vista and were told that 134a does just that to the copper core aluminum ones. Just passing it along.
    1990 735I (Auto) E32 Feb 1990 to Present
    1996 Z3 Roadster (5 Speed) E36/7 Jan 1999 to Dec 1999
    1983 733I (5 Speed) E23 April 1983 to Feb 1990
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  6. #6
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    I did some more google searches and that confirms it, some excerpts: r134a bubbles in sight glass

    I totally agree. The weight of the complete refrigerant charge is the most accurate way to charge the system. I've googled the subject and most of the technical articles have mentioned that in the days of R-12 refrigerant, the sight glass on top of the receiver-dryer would look clear when the system was right, indicating liquid refrigerant with no vapor bubbles. However, this is not applicable for R-134a . It uses a different type of oil, polyalkaline glycol (PAG). PAG oil does not fully emulsify the way the mineral oil used with R12 would in the past. The result is that the sight glass looks slightly cloudy even if the system is fully charged, except at very cool outside temperatures". The "sight glass charge inspection" can be used if the following conditions are met :
    Ambient temperature below 95 deg F.
    Humidity below 70%.
    High condenser fan speed (>=1500 rpm).(It's normal for some bubbles to appear in the sight glass of R134a systems in low fan speed).
    High-side system pressure below 240 psi (1640 kPa)
    Summarizing: R-134a is very hard to adjust the recharge rate to so it's usually weighed into the system rather than depending on the sight glass method.

    Regarding the bubbles that I mentioned previously, I meant that you should add refrigerant until you stop seeing bubbles in the sight glass. However, what I've heard from some engineers it that, when using R134a , bubbles may continue to appear in the sight glass despite the system has the adequate amount of refrigerant what may lead to refrigerant overcharging event. ... have commented that this may be related to the use of PAG oil. According to him, modern R134a unit no longer uses PAG oil (they use POE instead). However, I could not find any article that confirms that we can rely on sight glass indication when using POE oil.


    134a, Sight Glasses, and Bubbles https://autoacforum.com/messageview....&threadid=8642

    here in detail http://arrc.ebscohost.com/ebsco_stat...RANT_LEVEL.htm
    Figure 1: oil streaks, constant bubbles or foam. .....

    from Ferrarichat: Some people say that you don't use the sight glass in R134A systems to gauge whether the system is full or not. Some people say that it doesn't matter and you can use that sight glass to tell. From my experience (12 yrs of servicing and repairing a/c systems), I reckon you can use the sight glass to tell if an R134A system is fully charged or not. I can deal with some very minor bubbles in there, but for the most part I use pressures to tell if the system is right and the 'feel' test on the low side a/c pipes. But to answer your question, it's a yes from me. You can use the sight give you an indication of what is going on there. But you will definitely have to put some gauges on the system to get a better idea of the a/c performance.
    Shogun tricks and tips for the E32 series are HERE!

  7. #7
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    Just a thought to check out - your Heat Valve might be leaking, and sabotaging your cooling.

    Just feel the hose temperatures at the valve body beside the charging post in the engine bay.

  8. #8
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    Never have I seen an E32 and E34 that had that sight glass. Is this on later models 'coz my pre-90's doesn't have.

  9. #9
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    my 11/88 E32 750 has this sight glass. It is under this plastic cover just right next to the e-box http://www.meeknet.co.uk/E38/AC/Index.htm
    Shogun tricks and tips for the E32 series are HERE!

  10. #10
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    If the A/C system works but is just vaguely cold then it could well be short of gas - or - the airflow through the condenser is insufficient. When I changed my auxiliary fan you wouldn't believe how much junk was between the radiators, I was surprised it worked at all - pictures here:

    https://www.meeknet.co.uk/E31/timms_...eplacement.htm
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  11. #11
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    If you have replaced everything mentioned and charged the system properly and it blows cold and then in a few days its not as cold, then you have a leak in the system some where. Did the last people who charged the system add a dye? Bubbles in the sight glass are a sign the system is low on Freon. Its also always important to know what the high side and low side readings are after fully charging the system. I had the same issue 2 summers ago. Charged system w/dye and 2 weeks later not as cold. The dye is fluorescent and will illuminate with a blacklight. No signs of oil or dye under the hood or around the condenser so I removed the cover on the right side of the evaporator case and green dye every where. Replaced evaporator and expansion valve and have had no issues since. Good luck.

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