e30 A/C Relay question - no power to low pressure switch

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My 1987 325ic has not had working A/C since I've owned it (3 years), and last weekend I finally got the time to work on it, after months of on and off diagnosis.
It had a plugged expansion valve, so I replaced it and the drier and recharged the system with the R-12 I had recovered from it plus a little more (2.1 lbs according to the sticker). When I tested it I found that it would only work if I connected 12v to the compressor clutch directly. In this manner it works as it should - good low and high side pressures, and 40 degree air out of the vents.
After troubleshooting the low and high pressure switches (both were OK), I found that I did not have any voltage on the input side of the low pressure switch. However, when I depress the A/C switch on the dash, with the fan and vent control in the proper setting, the Aux fan turns on, so I know that part is working.
I then went to check the evaporator temp sensor - it measured 0 ohms at ambient temperature. the two wires that plugged into the evap temp sensor measured 0 volts (brown wire) and 7-8 volts (black/white wire).
I found the A/C control relay under the dash but do not know how to test it. It seems to be the point that power would go to the compressor clutch - it gets power on pin 3 when I activate the dash switch, and pin 4 energies the clutch when I apply 12v to it. I don't know where the other pins connect to - can anyone help me troubleshoot this before I buy a replacement for $70?
Thanks in advance.
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Sorry I can't help you with your problem, but I'm very curious on where you managed to find R12. AFAIK, it's virtually unobtainable now; however I would like a couple of pounds myself.
FloydR
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Floyd Rogers wrote:

I bought R-12 on ebay - it's selling high right now ($20-$30 per can), but if you purchase higher quantities or wait until the off-season you should be able to get it for around $15/can. Still high, but for now I'd rather keep it an R-12 system than convert it to R-134. Given that the e30 holds 2 pounds (less than 3 cans), it's not that bad if you do it yourself. I found an older R-12 reclaimer from a service station; it was very inexpensive and it makes it possible for me to open up my own systems.
You need to be EPA certified to purchase R-12, unless you verify that you are buying it for resale. I got my EPA certification online for $20 I think, and actually learned a few things getting ready for the test. I can send you the link if you are interested.
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Floyd Rogers wrote:

I bought R-12 on ebay - it's selling high right now ($20-$30 per can), but if you purchase higher quantities or wait until the off-season you should be able to get it for around $15/can. Still high, but for now I'd rather keep it an R-12 system than convert it to R-134. Given that the e30 holds 2 pounds (less than 3 cans), it's not that bad if you do it yourself. I found an older R-12 reclaimer from a service station; it was very inexpensive and it makes it possible for me to open up my own systems.
You need to be EPA certified to purchase R-12, unless you verify that you are buying it for resale. I got my EPA certification online for $20 I think, and actually learned a few things getting ready for the test. I can send you the link if you are interested.
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Um, well, err, it's good that you know what you're doing but the bad news with A/C systems is in a car this age you end up playing "follow the bouncing fault" and as soon as you fix one thing the next weakest part dies. That may or may not get old real quick depending on your patience.
The only sure way you're gonna get the A/C to work flawlessly for the next decade is to fix everything at once and be done with it.
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True, but then I would miss the fun of the diagnosis! I think I would rather own an almost 20 year old BMW that I can fix myself than a newer one that I have to pay for and cannot.
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I hear ya and I agree with the sentiment. Change all the hoses you can at the least. Although they're expensive from the dealer they're standard hoses with standard fittings andy any good A/C shop can make them up for you cheap.
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Err, it appears to be an electrical fault. Leaks can be a different matter.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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Understood. But the statistical likelyhood of an A/C system that old having only one fault is near zero. I must be getting old and crusty, but I've seen this is many times with 20+ year old cars that maybe it's worth repeating.
Or not.
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I have not had to locate this particular relay but assuming it is a 4 pin relay (if not I'll look up the specs on it), 2 pins power the coil that operates the relay and the other two switch the load. The fact that you can put 12v to pin 4 and power the compressor clears the high/low pressure switches. The fault is around that relay. Which pin (1 or 2) has power when the key is on? One should be 12v and the other is connected to ground. If the relay has more than 4 pins this will not be the case. The coil temperature sensor most likely controls the ground side of the relay. Might alter the 12v side instead but that would not be common practice. Check this out and get back to me. A fully working A/C system is right around the corner....
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Standard Bosch/Lucas relays of that era are labelled :-
85 coil 86 coil 30 or 30/51 common 87 normally open 87A normally closed
The five pin changeover type can often be used instead of a four pin simple on off type as the bases are usually identical with just no connection to the NC terminal.
However on the E30 I *think* the relays just control the fan. The clutch is switched directly by the main system switch via of course the pressure switches.
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The relay is 6 pin, and when I looked inside (I was able to open the case) I found it had the relay normal coil and points, but also a small circuit board with some digital components, some capacitors, and a transistor. It looks like the power from the dash switch activates on side of the coil, but the other side has to go through the transistor to get ground - so I would guess that the digital circuit takes inputs from 3 of the other pins and then provides ground to the coil when the conditions are right.
I'm waiting on my service manual to arrive in the mail (probably next week); I'm hoping it will tell me what the wires go to. I will be going out in a bit to see if 12v and ground are on the pins I think they should be on.
I don't think the switch on the dash directly powers the clutch and pressure switches in series because the compressor clutch wire comes back to this relay.- it has to be providing some logic as to when it can be turned on.
I think at least I can do some tests on the relay - if I plug it in I can use my meter to check for grounds and voltage.
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I had, but have lost, an article I wrote describing pinouts of all commonly used relays on German cars. It should have a number on it someplace - two digits - that tells you what "type" it is. If you can find that and lemme know I can find out what the pinouts are.
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Here is a picture of the replacement part: http://oem.thepartsbin.com/parts/thepartsbin/wizard.jsp?year 87&make=BM&model25-IC-001&category=All&part=A/C%20Control%20Relay&dplse
Mine says Bosch and had the number 058 in a circle next to Bosch.
It's p/n is Bosch: 1 147 328 093 Behr: 90.943.01.439 BMW: 1.381.496.2
On the back of the case is the number 652 in white marker or stamp.
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My source is away till aug 28 and google finds nothing and archive.org is down (there's a chance i could find my old article there).
I'm drawing at blank moment sorry.
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Here's an update. My relay did not match the one that Yvan sent, but the wiring diagram helped me get an idea of how it worked. The function is similar, but the pin numbers and wire colors are not the same.
My evap temp regulator is pinned like this:
pin 1 (brown) - ground pin 2 (bk/yel) - unknown pin 3 (brown) - ground pin 4 (bk/violet) - 12v when dash button on pin 5 (violet) - to pressure sensors and clutch, I think pin 6 (bk/white) - to evap temp sensor
Initially I thought my high pressure sensor was bad because it was open during normal conditions, unlike the low pressure sensor which is closed under normal conditions. So, I jumped the connectors at the high pressure switch. In this manner, if I jumped pins 5 and 4 with a wire (temp regulator out of the picture) the clutch would operate with the dash switch and run constantly.
However, reading the digram showed me that the high pressure switch might be open under normal conditions, so I removed it's jumper, plugged in the wires, and reconnected the regulator. This sort of worked - now the evap temp regulator clicks when I turn on the A/C, but there is no power at the clutch, even though there is power at the sensors. Removing the requlator and jumping pins 5 and 6 with wire does the same thing - power at the sensors but not the clutch.
I'm going to wait for my manual to arrive and see if they are the same. There must be another sensor or connection in there that is not being made.
This is an unusual circuit - it seems to be energizing by providing a ground, and there is a feed back loop that deactivates it if the high pressure switch closes.
Does anyone know what state the pressure switches are in when the state is normal operation (proper pressures)?
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jrm wrote:

I have sent you a pdf of the Heating and Air Conditioning electrical sections for the 87 e30. Hopefully it will help a bit.
Cheers, Bob
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Please email to jmweb<remove me>@alltel.net; I have to change my profile as the dreamscape.com address is no longer functioning.
Thank you for the info.
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Another work session, and now my A/C is working as it should. 35 degree air at highway speeds, and the a/c compressor cycling as it should.
I confirmed that with the high pressure switch connected (as an open), the clutch would not engage with the evap temp controller in place or with it removed and a jumper placed between pins 4 and 5. So, at least I had consistency.
I went back to the assumption that the high pressure switch is supposed to be closed in normal operation and disconnected its wires, putting a jumper in place again. I then put the evap temp controller back in place, and tried it. The evap temp controller clicked in, and the compressor clutch engaged. I had 12v at the high pressure switch, low pressure switch, and clutch.
So, what I'm left with from this excercise is that after I replaced the plugged expansion valve and recharged the system, the relay in the evap temp sensor was stuck after years of not being used, or the connectors were corroded. After I took everything apart and moved the relay contacts by hand, and with all the plugging and unplugging, things finally were cleaned up and making contact.
One thing that is important for someone troubleshooting this; because of feedback and some parts of this circuit getting enabled by a ground, if you disconnect the low pressure switch to see if 12v is present, I think the evap control relay will disconnect and the voltage will be removed. I was doing this at first. Check for voltage with the connections in place, and scrape with your probe to make sure you are getting through any corrosion. On this car, it is not a simple +12v --> Switch --> low psi switch --> compressor clutch circuit. One post I read said to test the evap temp sensor by applying 12v to one of it's leads; in this circuit that would short directly to ground if the sensor was working.
Thanks to all who helped. I hope someone else can use this as well. Let mw know if you want any working diagnostic info.
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Nedavno jrm pise:
| I found the A/C control relay under the dash but do not know how to | test it. It seems to be the point that power would go to the | compressor clutch - it gets power on pin 3 when I activate the dash | switch, and pin 4 energies the clutch when I apply 12v to it. I don't | know where the other pins connect to - can anyone help me troubleshoot | this before I buy a replacement for $70?
You are looking at evap temp regulator.
pin 1 (blk-wht) goes to evap temp sensor, pin 2 (blk-yel) goes to plug and then to high pressure switch (blk-red) pin 3 (blk-vio) as you noticed gets input from a/c on/off switch pin 4 (brn) ground pin 5 (vio) goes to plug and then to high pressure switch (blk) pin 6 (brn) ground
This is how it looks like on the wiring diagram I have. If you are sure that you applied 12V to pin 4 and did not burn anything than yours must be different. If not perhaps this might help you. I downloaded this wiring diagram (for 1987 325e) from some Russian site, so no guaranties. I can mail it to you if you want (I will try mail address from your post).
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