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    Converting to r134a? read this before doing it...

    This info is relevant for cars that came originally with two pressure switches (I think is pre 1989)
    (I kindly ask more experienced forum members to correct me if necessary).

    Alright, so I just did my r134a conversion following the BMW TIS. I got the new high pressure switch (64538390971) with the new dryer (64538391025), replaced o-rings here and there, and changed the oil/lubricant in the compressor. However the pressure switch splice deal is not clearly explained in the TIS.

    The TIS says you should cut and join the cables from one of the pressure switches but it does not specify which or how. Here is what I did.

    Please see the attachment which are the electrical diagrams and explanation of the circuit for the original set-up.

    ORIGINAL SET UP
    The cables that go to the high pressure switch are three:
    1h. Black with white stripe
    2h. Black with yellow stripe
    3h. Black
    2h and 3h go together at the connector

    The cables that go to the low pressure switch are three:
    1L. Black with Red stripe
    2L. Black with Red stripe
    3L. Black
    1L and 2L go together at the connector

    CONVERSION SET UP
    • 1h, 2h, 3h are ALL soldered or crimped together
    • The new high pressure switch has two cables, one connects to 1L and the other to 2L+3L (through a connector).


    The rationale is that by doing this the old high pressure switched is eliminated and the new high pressure switch replaces the old low pressure switch. In this way the A/C Clutch Monitor Input and the Compressor Control remain connected to the rest of the system via the new high pressure switch.
    Attached Files
    Last edited by chrisca70; 12-17-2014, 05:15 AM.

    #2
    Since nobody has thanked you yet, I would like to take the opportunity to do so. THANK YOU. This thread probably hasn't seen much action due to the season, but your input is appreciated! I myself will be using this next month when I do a full conversion.

    Comment


      #3
      I have a 84 eta. What parts are needed for the r134a conversion? I also got a 89 325i for parts. Anything i can use from there?

      Btw thanks for the info cause i know i'll be needing too and summer comin up soon i better get it done now before i die in the heat lol

      Comment


        #4
        Originally posted by chrisca70 View Post
        This info is relevant for cars that came originally with two pressure switches (I think is pre 1989)

        (I kindly ask more experienced forum members to correct me if necessary).



        Alright, so I just did my r134a conversion following the BMW TIS. I got the new high pressure switch (64538390971) with the new dryer (64538391025), replaced o-rings here and there, and changed the oil/lubricant in the compressor. However the pressure switch splice deal is not clearly explained in the TIS.



        The TIS says you should cut and join the cables from one of the pressure switches but it does not specify which or how. Here is what I did.



        Please see the attachment which are the electrical diagrams and explanation of the circuit for the original set-up.



        ORIGINAL SET UP

        The cables that go to the high pressure switch are three:

        1h. Black with white stripe

        2h. Black with yellow stripe

        3h. Black

        2h and 3h go together at the connector



        The cables that go to the low pressure switch are three:

        1L. Black with Red stripe

        2L. Black with Red stripe

        3L. Black

        1L and 2L go together at the connector



        CONVERSION SET UP

        1h, 2h, 3h are ALL soldered or crimped together
        The new high pressure switch has two cables, one connects to 1L and the other to 2L+3L (through a connector).

        The rationale is that by doing this the old high pressure switched is eliminated and the new high pressure switch replaces the old low pressure switch. In this way the A/C Clutch Monitor Input and the Compressor Control remain connected to the rest of the system via the new high pressure switch.


        Wouldn't wiring the switch per your directions either result in the Motronic Control Unit or the A/C Compressor receiving power independent of the cut-out switch position depending on which black/red wire (either 1L or 2L) are connected to the black wire (3L)?

        Shouldn't the wiring be: 3L to one cable from the cut-out switch and 1L and 2L to the other side of the switch?. Is the new high pressure switch both a low pressure and high pressure switch?
        Last edited by Code808; 03-12-2015, 09:34 AM. Reason: To ensure orignial remarks are quoted

        Comment


          #5
          Originally posted by chrisca70 View Post
          This info is relevant for cars that came originally with two pressure switches (I think is pre 1989)
          (I kindly ask more experienced forum members to correct me if necessary).
          I have a 1989 325i (02/89 build) and my drier had two switches attached. I am going to be wiring up the new switch tomorrow following your directions. It's the last thing I need to do before firing up the car and completing the fill. I have 12 oz in the system now that I was able to get in without having to fire up the car.

          I replaced evap, expansion valve, drier, compressor (Valeo R134 specific), PF condenser with Spal fan, ALL o-rings, and removed all lines and brought to a shop to have them flushed. I have high hopes for a very cold system!

          Comment


            #6
            So I wired up the new pressure switch a week or so ago and filled the system. I was doing some work under the hood today and took note of the compressor to see if it was cycling. It was not. When I press the snowflake the compressor kicks on and cold air comes from the vents but it doesn't cycle like it's supposed to. I'm wondering if it has anything to do with the revised pressure switch wiring? Any help would be greatly appreciated.

            Comment


              #7
              Unless the cut in-cut out pressure ratings of your switches are not consistent with the new operating pressures I don't see any reason to change them. Pressures are more dependent on the compressor anyway so if you are just doing a flush, expansion valve and r134a recharge there's a good chance your old switches will serve.
              Deck Lid and soft top Shocks on hand

              Seat shocks on hand for immediate shipment
              https://www.r3vlimited.com/board/sho...86#post4944786
              Alice the Time Capsule
              http://www.r3vlimited.com/board/showthread.php?t=360504
              87 Zinno Cabrio barn find 98k and still smells like a barn. Build thread http://www.r3vlimited.com/board/show...20#post3455220

              Comment


                #8
                Originally posted by jeffnhiscars View Post
                Unless the cut in-cut out pressure ratings of your switches are not consistent with the new operating pressures I don't see any reason to change them. Pressures are more dependent on the compressor anyway so if you are just doing a flush, expansion valve and r134a recharge there's a good chance your old switches will serve.
                I changed everything exactly like you did. Even used the exact same components and stole your genius idea for the Spal fan mounting. My new drier only has one port so I was forced into tying the two sensors into one anyhow.

                Comment


                  #9
                  I get Behr driers from autohausaz and they all,have multiple ports. Having said that, if it works that's what counts.
                  Deck Lid and soft top Shocks on hand

                  Seat shocks on hand for immediate shipment
                  https://www.r3vlimited.com/board/sho...86#post4944786
                  Alice the Time Capsule
                  http://www.r3vlimited.com/board/showthread.php?t=360504
                  87 Zinno Cabrio barn find 98k and still smells like a barn. Build thread http://www.r3vlimited.com/board/show...20#post3455220

                  Comment


                    #10
                    Originally posted by jeffnhiscars View Post
                    I get Behr driers from autohausaz and they all,have multiple ports. Having said that, if it works that's what counts.
                    I also got a Behr drier, but not from Autohaus. Think mine came from ECS or something. At any rate, it has just one port and my compressor runs 100% of the time the snowflake is engaged. It has to be a product of the wiring advice offered in the original post. Just trying to get some feedback from others who have wired in the single sensor to see how they did it.

                    Comment


                      #11
                      the compressor should run all the time and the sensors are high/low safety cut offs. Hopefully they never do anything.
                      Deck Lid and soft top Shocks on hand

                      Seat shocks on hand for immediate shipment
                      https://www.r3vlimited.com/board/sho...86#post4944786
                      Alice the Time Capsule
                      http://www.r3vlimited.com/board/showthread.php?t=360504
                      87 Zinno Cabrio barn find 98k and still smells like a barn. Build thread http://www.r3vlimited.com/board/show...20#post3455220

                      Comment


                        #12
                        Originally posted by jeffnhiscars View Post
                        the compressor should run all the time and the sensors are high/low safety cut offs. Hopefully they never do anything.

                        Then what makes the compressor cycle during operation? When filling the system on my truck I can watch the manifold gauges increase in pressure and then the clutch wild disengage and the pressure would slowly drop and then at some pre-determined PSI the clutch would re-engage and this cycle would repeat itself. Each cycle happened every couple minutes I guess or maybe a little more frequently. My E30 compressor clutch stays engaged 100% of the time the the pressures barely fluctuate on the gauges during operation. I'm a little confused.

                        Comment


                          #13
                          Originally posted by jph View Post
                          Then what makes the compressor cycle during operation? When filling the system on my truck I can watch the manifold gauges increase in pressure and then the clutch wild disengage and the pressure would slowly drop and then at some pre-determined PSI the clutch would re-engage and this cycle would repeat itself. Each cycle happened every couple minutes I guess or maybe a little more frequently. My E30 compressor clutch stays engaged 100% of the time the the pressures barely fluctuate on the gauges during operation. I'm a little confused.
                          When you start with an empty system the low pressure switch will prevent the compressor from engaging until the pressure reaches the set point, which in our cars is 25lbs. With the engine off you will get a fill to static pressure which will be about the same as ambient temp on both sides (so if it's 80 out you should have 80lbs on high and low sides). Now you start your engine and let the compressor do the rest of the charging.

                          Having said that, some vehicles have additional cut offs so the compressor will cycle the way your home ac does....ie reach a certain temp the system goes off which will, of course make the pressure drop. keep in mind that at home both inside and outside fans go off when the system cycles, whereas in your truck, the inside fan keeps running regardless of the compressor.

                          I hope that helps :)
                          Deck Lid and soft top Shocks on hand

                          Seat shocks on hand for immediate shipment
                          https://www.r3vlimited.com/board/sho...86#post4944786
                          Alice the Time Capsule
                          http://www.r3vlimited.com/board/showthread.php?t=360504
                          87 Zinno Cabrio barn find 98k and still smells like a barn. Build thread http://www.r3vlimited.com/board/show...20#post3455220

                          Comment


                            #14
                            Your a pal. This wiring saved my butt- the TSB is confusing and the 134a thread doesn't really give a clear answer.


                            Thanks!!!!
                            555Garage - Kingston, PA

                            '13 BMW e70 X5 35d
                            '95 BMW e34 525i
                            '92 BMW e30 325i S52 Vert (Quade the Vert)
                            '92 Range Rover Classic
                            '90 Range Rover Classic
                            '89 BMW e30 325i Coupe (The DIRTY30)
                            '81 VW MK1 Rabbit Caddy Diesel
                            '76 Honda CB550K Cafe/Brat
                            '67 Pontiac LeMans
                            '24 Model T Depot Hack
                            ....And a bunch of Motobecane, Puch, Garelli, Batavus and Honda 49cc-78cc Mopeds...

                            Comment


                              #15
                              Originally posted by jph View Post
                              Then what makes the compressor cycle during operation? When filling the system on my truck I can watch the manifold gauges increase in pressure and then the clutch wild disengage and the pressure would slowly drop and then at some pre-determined PSI the clutch would re-engage and this cycle would repeat itself. Each cycle happened every couple minutes I guess or maybe a little more frequently. My E30 compressor clutch stays engaged 100% of the time the the pressures barely fluctuate on the gauges during operation. I'm a little confused.
                              Your Truck has a more efficient ac system, so as your evaporator reaches 32f (freezing) the thermo switch will cut the compressor to prevent damage/ frost blockage building up.

                              Our e30s have this too,(actually all AC systems do). My AC will cycle at lower ambient temperatures or higher RPM, maybe because i installed a PF condenser.

                              I got this PDF from glucklich21, it has detailed instructions of what wires to cut/splice. https://docs.google.com/file/d/0B4vP...CNO6w-8O&pli=1


                              And here is his thread
                              http://www.r3vlimited.com/board/showthread.php?t=246743
                              Last edited by cabriodster87; 06-08-2015, 08:00 AM. Reason: add retrofit PDF
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                              Reich und Roll!

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