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    A/C pressure switch problem(i think)

    So i just got done converting to R134, The right way, and now im having an issue with the compressor clutch not kicking in when i hit the snowflake button, although something happens, because i hear the revs go up a little in the engine bay when i hit the button. Oh and the snowflake doesnt light up blue no matter how the flaps are positioned etc. I did some troubleshooting and the clutch kicks in when i jump the plug for the pressure switch. When the switch is jumped the a/c blows pretty cold, today it is 95ish degrees out and i was sufficiently cooled in the car, could be a little colder though. Here is what all i did in the conversion.

    Replaced condenser with parallel flow one
    replaced all o rings
    New 4 season evaporator
    New Expansion r134 expansion valve
    New style drier for single hi/lo switch
    New hi/lo switch (This One)
    Spliced pressure switch harness with terminal and wire set i got from the dealership, to accept new terminal style for new pressure switch.

    The system had already been converted a bit by PO so i didnt need to add pag oil.

    After i put it all together i added 12 oz of r134, then a few ounces of a stop leak concoction(which worked amazingly btw) and then added about 3-5 more ounces of refridgerent until the guage manifold read around 48psi, which is in the full zone. Idk if this makes a difference, but when the car is turned off and the gauges are hooked up, the pressure on the low side skyrockets all the way to the top.
    I remember seeing somewhere that it should take about 25-28oz of r134.


    Any help on why it wont run unless i jump the safety switch would be appreciated
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    #2
    The system should have taken 30oz of R134a (.9 x 2.15lb of R12). You have about half (~15oz) of the normal charge. Even so that should be enough to close the low pressure switch. Did the car originally have the separate pressure switches? If so did you short the wires on one of the connectors? Those were wired in series and have to short one pair for the other pair to work.

    If you don't have a good way to charge by weight, charging by pressure is the alternative. There you charge until the high side pressure is 2.3 time the ambient temp in temperature in degrees F, with the engine at 2500rpm and the aux fan jumpered for high speed. If the expansion valve is working and the compressor is in good condition low side pressure should be in the low 40's.

    In this case, with what you have replaced, I'm thinking the compressor is badly worn. It is possible that the expansion valve is bad and stuck wide open, but that is unlikely. I say that because your low side pressure went too high on a half charge. If you fully charge the system I'll be the low side pressure will be 20psi or more too high.

    Always disconnect the low side gauge before turning the A/C off. The pressures will equalize quickly and you can damage the low side gauge.
    The car makes it possible, but the driver makes it happen.
    Jim Levie, Huntsville, AL

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      #3
      Oh yes i forgot to mention i cut the connectors off the old low side switch, and then soldered them together and then heat shrinked them as the original bmw bulletin said to do. Im pretty sure i have an original compressor, or at least a pretty old bmw replacement. it has a bmw tag and everything on it.

      Could it be possible that the PO put too much oil in their? i disconnected the whole system, so any oil that was still in the system would have been in the compressor.\

      And also im guessing that if jumping the terminal for the switch works, that means my soldering for the splice it good yea?
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        #4
        I don't know if it's right, but i monitored lowside tube to lowest temp.
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          #5
          Oh and when i spliced the new terminal to the old one, there was one connector that had 2 wires going to it, and the other just had one. I soldered the 2 wires to one of the wires for the new connector, and then the other 1 wire to the other new wire. Was that correct? i searched everywhere and i couldnt find anything that said that was wrong
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            #6
            Last edited by cabriodster87; 08-31-2012, 03:35 PM.
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              #7
              Yea i used that guide, but all it says about the switch is "connect the switch" the person that did the guide already had the rigth terminal
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                #8
                my bad
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                  #9
                  is it consistently not engaging or every once in a while not engaging?

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                    #10
                    OK i remember, you have to really tighten down the switch to the drier. it wasn't reading pressure.
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                      #11
                      Use an ohmmeter to make sure the low pressure switch is closed.

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                        #12
                        Originally posted by markt51 View Post
                        Oh yes i forgot to mention i cut the connectors off the old low side switch, and then soldered them together and then heat shrinked them as the original bmw bulletin said to do. Im pretty sure i have an original compressor, or at least a pretty old bmw replacement. it has a bmw tag and everything on it.

                        Could it be possible that the PO put too much oil in their? i disconnected the whole system, so any oil that was still in the system would have been in the compressor.

                        And also im guessing that if jumping the terminal for the switch works, that means my soldering for the splice it good yea?
                        It does sound like you dealt with the switch wiring correctly. The wiring for one of the separate switches gets shorted and the other goes to the new dual switch.

                        As to the oil. When converting to R134a, the compressor must be removed, the oil drained, and the proper amount of PAG oil put in the compressor. Some folks say to put half of the oil in the compressor and the other half in the dryer. I just put it all in the compressor. But the oil isn't your problem.

                        What is the high side pressure and the ambient temperature when the engine is at 2500rpm with the aux fan on high speed?
                        The car makes it possible, but the driver makes it happen.
                        Jim Levie, Huntsville, AL

                        Comment


                          #13
                          I used that same ilustration that Cabrio posted, so i did that right. Ill have to check high side pressure tomorrow. But To answer BMWStephen, Its constantly not engaging, unless i jump the terminal. I hand tightened the switch pretty snug, maybe ill get a crecent wrench and get it down tighter.
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                            #14
                            Originally posted by markt51 View Post
                            I used that same ilustration that Cabrio posted, so i did that right. Ill have to check high side pressure tomorrow. But To answer BMWStephen, Its constantly not engaging, unless i jump the terminal. I hand tightened the switch pretty snug, maybe ill get a crecent wrench and get it down tighter.
                            How tight the switch is has everything to do with leaks and nothing to do with operation of the switch. It sounds to me like the system is just undercharged to the point that the low pressure switch is disabling the compressor.
                            The car makes it possible, but the driver makes it happen.
                            Jim Levie, Huntsville, AL

                            Comment


                              #15
                              k. Tomorrow ill try to tighten the switch, and then charge it more. I just stopped filling it at 15oz because of what the gauges read.
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