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

"jrm" wrote

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

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.

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.

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.

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.

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.

Err, it appears to be an electrical fault. Leaks can be a different matter.

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.

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....

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.

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.

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.

Here is a picture of the replacement part:

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.

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).

This is great! Thank you so much. I'm not sure I connected 12v to pin

1 - I lost track of the pins and couldn't remember once I got in the house to post the question. I know that one of the corner pins went to 12v when I pushed the dash switch, and the one right next to it went to the AC clutch (via the pressure sensors). So, they were probably pin 3 and pin 2.

Please send to snipped-for-privacy@alltel.net after removing the brackets what's inside.

This is great! Many thanks. I'm not sure I connected 12v to pin 1 - I lost track of the pins and couldn't remember once I got in the house to post the question. I know that one of the corner pins went to 12v when I pushed the dash switch, and the one right next to it went to the AC clutch (via the pressure sensors). So, they were probably pin 3 and pin 2.

Please send to snipped-for-privacy@alltel.net after removing the brackets and what's inside.

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.

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)?

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