Replacing AC compressor and fan relay

billpatterson

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Hi there
I have tested the original relay and I am getting no reading for resistance between 85 and 86; this indicates its toast, according to relay testing websites. So, I am going to replace it with a standard Bosch relay. I have rad some have done this on the Forum. I have attached a PDF of the original relay and the new Bosch relay and proposed wiring. I am uncertain about some wiring though; please have a look and I look forward to your advice.

Regards,
Bill

AC relay new relay wiring copy.jpg
 

billpatterson

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The relay does not send power to the compressor, only the blower. The trigger wire from the temp switch branches off at the relay spade and goes direct to the compressor.

Hi Chris

I wired a new relay following instructions from Ohmess. And I have checked all wiring from the 12v lead to checking continuity in the trigger wire from the AC temp switch. It all seems OK. Still no AC pump or condenser fan turning on when the turning the temp switch. It was working wonderfully for a while and the only thing I did in that area was reinstall the glove box and passenger valence panels; I've looked behind the AC switch and radio panel; nothing seems amiss and there's 12v coming to the temp switch/ I hear the relay behind this panel click/turns off the heater fan for the AC fan.

Any thoughts or suggestions for diagnosis are appreciated. How many volts should there be along the AC pump trigger wire when the AC switches are on and set to cold? I think its a good approach to back track.

Also, what does this 'module' do? Finding info on it is proving very difficult.

Regards,
Bill


IMG_3067.JPG
 
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sfdon

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That module turns on the auxiliary fan when your engine gets too hot.
 

sfdon

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Jesus from Espana can give you the schematic and the connections and wire colors and locations better than I.
I take them out and he installs that module.
It measures the resistance of the sensor for the temperature gauge and activates the auxiliary fan. You should see two brown/white wires at the sensor instead of just one because of this unit. Only late models have it.
there is a schematic on the silver label.
 
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billpatterson

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I would check for power coming from the relay to aux fan, and inline fuse to relay in front of radiator.

Hi Chris,
I did check the power coming from the battery to the relay; its good.

I assumed the power to the aux fan wouldn't be an issue given the new and checked relay. Though its not bad to be a lil skeptical so I will check that...

THX
 

billpatterson

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Jesus from Espana can give you the schematic and the connections and wire colors and locations better than I.
I take them out and he installs that module.
It measures the resistance of the sensor for the temperature gauge and activates the auxiliary fan. You should see two brown/white wires at the sensor instead of just one because of this unit. Only late models have it.
there is a schematic on the silver label.

Hi sfdon,

My bavaria is a March 1973 baby.

How does one bypass / take out the module from the AC system? Are there issues to be aware of?

Regards,
Bill
 

billpatterson

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That module wasn’t added to the e9 until MY74. Just unplug it or disconnect wire from temp sender in radiator. Are you sure your aux fan works?
Hi Chris

The car does not have a temp sensor in the radiator. Interesting!? Yes...the fan runs; the AC system was working recently. Not sure why the change. I started with the relay and found it to be bad; replaced it and still not working. I thought I would ask about the black box because I did not know its function.

THX
 

HB Chris

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You shouldn’t have that feature in a 73, maybe it was added, is there a second sensor in your water divider by the thermostat?
 

billpatterson

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Hi Chris
I was going to start a Conversation with you but then thought thats the opposite of the Forum concept. They are for people to learn, from either asking questions, replying or reading.

-------

I have read that AC systems were installed at the BMW dealers when a customer bought a car and wanted AC.

There is no second coolant sensor or the 'bung' for one on my coolant divider.

Humbly, I do not pretend to understand electrics. Again, another wonderful thing about Forums like this one cuz there's enthusiasts out there that know about electrics on these cars.

-Bill
 

HB Chris

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Bill, Here is the pre-74 A/C wiring.

e9AC wiring w legend.jpg


I have a couple of your rectangular can relays if you need one. The e3 used that style, the e9 used the round can style. As you know, power from battery is 30, power the aux fan in front of rad is 87, 85 and 86 are the trigger from temp switch and ground, doesn't matter which is which. Temp switch to 86 branches off to the compressor and doesn't use the relay. Does interior A/C fan work? It send power to the temp switch, if it isn't working the issue is upstream. I have a friend whose A/C wasn't working. I traced all of the works, checked continuity and such and it was his load shed relay! I thought those never go bad, first time I had seen that. BTW, the changeover relay turns off heater fan when A/C is turned on, in 74 and later cars the Fan speed does this instead, switches are different and can't be swapped.
 

billpatterson

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Hi Chris

Do you think the fact that my car does not have the 2nd temp sensor is a problem? The AC system was working before so I tend to think its not part of the problem.

Yes...my interior AC fan works; when the AC fan switch is switched on, the heater fan turns off and the AC fan spins (via the changeover relay I presume?). The temp switch also work (when the AC was working a few weeks ago).

Thank you...would you please send me one of the rectangular relays? I presume thats the load shed relay? We can start a Conversation with the details.

I think I will replace the 12v lead between the battery and relay too and include a good fuse.

Much appreciated,
Bill
 
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HB Chris

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The load shed relay is under your dash by driver's A pillar, I have pics of e9 relays in the faq section but not e3. It might be a round can relay or square plastic relay but not the large rectangular one for the aux fan. If you touch these relays while turning your key on you should feel it click. And post a pic of those relays, might be the same as e9. Here is 73 e9.
Relay 1 Wiper.JPG
Relay 2,3,4.JPG
 
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billpatterson

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Hi Chris
It was very nice talking to you! Thanks you for your time!

Here is a pic of the relays under the dash/above the fuse panel on my E3 (and they both click when the key is turned on). Also, the AC fan when turned on does switch off the heater fan :) (I can hear that relay clicking too).



IMG_3072.JPG
 
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Ohmess

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Bill -- good point about having this stuff in the forum itself. Further to this suggestion, here is the suggestion I just sent to you in our conversation:

Well, a couple of things come to mind. First, pull the wires from terminal 30 and terminal 87 on the relay, and check the function of the relay itself. To do this, make sure both the fan switch and the temp switch are not bottomed out, and test for continuity between terminals 30 and 87. You should have continuity. If not, check your ground (likely at terminal 85). Then check for current (s/b 12v) at terminal 86 with the fan and temperature switches in this same position.

Next, check for continuity on the terminal 30 wire, with it disconnected at both ends. If you have continuity, then check the resistance and let's look at how much resistance you have in that wire.



As to that black box, that is merely another way to initiate the fan in front of the radiator. The fact that this second method of initiating the fan is disconnected should not have any adverse effect. That said, this secondary mechanism is beneficial, and I added a temp switch and a relay to my car to do what this box does in yours.
Bill, Here is the pre-74 A/C wiring.

View attachment 121614

I have a couple of your rectangular can relays if you need one. The e3 used that style, the e9 used the round can style. As you know, power from battery is 30, power the aux fan in front of rad is 87, 85 and 86 are the trigger from temp switch and ground, doesn't matter which is which. Temp switch to 86 branches off to the compressor and doesn't use the relay. Does interior A/C fan work? It send power to the temp switch, if it isn't working the issue is upstream. I have a friend whose A/C wasn't working. I traced all of the works, checked continuity and such and it was his load shed relay! I thought those never go bad, first time I had seen that. BTW, the changeover relay turns off heater fan when A/C is turned on, in 74 and later cars the Fan speed does this instead, switches are different and can't be swapped.
Chris - I told Bill to keep the ground at terminal 85 and to combine the two wires he had on the terminal 86a anc 86c connections of his old relay onto terminal 86.
 

sfdon

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I use a factory 81* sensor and a factory diode on every car.
When the engine starts to overheat the fan comes on but leaves the AC alone.

fuse holder
fuse
sender
diode
wire
connectors

35 bucks of parts for peace of mind.
 

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billpatterson

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Bill -- good point about having this stuff in the forum itself. Further to this suggestion, here is the suggestion I just sent to you in our conversation:

Well, a couple of things come to mind. First, pull the wires from terminal 30 and terminal 87 on the relay, and check the function of the relay itself. To do this, make sure both the fan switch and the temp switch are not bottomed out, and test for continuity between terminals 30 and 87. You should have continuity. If not, check your ground (likely at terminal 85). Then check for current (s/b 12v) at terminal 86 with the fan and temperature switches in this same position.

Next, check for continuity on the terminal 30 wire, with it disconnected at both ends. If you have continuity, then check the resistance and let's look at how much resistance you have in that wire.



As to that black box, that is merely another way to initiate the fan in front of the radiator. The fact that this second method of initiating the fan is disconnected should not have any adverse effect. That said, this secondary mechanism is beneficial, and I added a temp switch and a relay to my car to do what this box does in yours.

Chris - I told Bill to keep the ground at terminal 85 and to combine the two wires he had on the terminal 86a anc 86c connections of his old relay onto terminal 86.

Hi Ohmess, Chris and sfdon!

Thanks! I will do these tests and report back once the car is back from the out of province road inspection and truly annoying high pitched muffler vibration mystery tour.

Appreciated,
Bill
 
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