Aux fan / AC / defogger question

[Chokingdogs]

So I understand the aux fan kicks on whenever the AC clutch is engaged, it should also ( I assume ) do the same when the defroster is turned on since the AC comes on with that. Is that the case, AC on when defrost running, and thus aux fan too? Does it matter what the ambient temps are, either outside or in the cabin taken from the CCU sensor?

It's right cold outside now, and when checking to see if the aux fan comes on with the AC turned on, I got nothing, no fan and the clutch on the compressor not engaged. I assume that's due to the CCU detecting the cabin is well below any need for colder air.

When I turned the defogger on, same deal, no fan and the clutch was freewheeling. That doesn't seem right?

Long story short here, I've had the FDM for a little over a year with no issues, up until last week. Sitting in a parking lot idling I heard/felt a couple popping/buzzing noises and noticed the needle had moved past halfway. Shut car off and looked around. No leaks, nothing in the coolant, no coolant smell out the exhaust. Did the AC test and compressor kicked on along with the fan, but they both stopped after maybe 10 seconds. Got back on the highway and was needle pegged solid at 12......until I hit DC traffic, and it started to creep up after 15 minutes or so in stop and go. Got moving again and it went back to 12. Nothing since, but I haven't had an extended time in S&G traffic.

Haven't jumped the connector at the rad sensor to test high/low aux fan function, yet. I'm wondering if I might have two separate things going on, something with the AC compressor, and an aux fan deal, and the popping/buzzing sound was maybe a relay for one or both croaking? I have not heard that sound since that one time.

Any thoughts?

[shogun]

This is how it works on my E32, and I assume it should be same on your 3.

aux fan kicks in automatically when the AC is switched on.
The aux fan also serves as a backup for the cooling system, when the temperature reaches (depends on the sensor installed) 196F (91C) degrees the aux fan will spin in low speed, when the temperature reaches 210F (99C) the aux fan should spin in high speed mode.

If the runs only when powered directly by the jumpered connector amd hot coolant is circulating through the radiator, the radiator switch is faulty. Use a new gasket ring (or crush ring) when replacing the switch.
Wires jumpered............Test conditions......Test results
Violet/grey and brown......ingition ON.....fan runs on low speed
Black/grey/yellow OR ignition ON.....fan runs on high speed
Black/grey and brown

If the fan does not run when powered directly, check for battery voltage at the switch connector with the ignition on. If battery voltage is not present, check fuse #.. (low speed) and fuse #.. (high speed). If no faults are found, remove the relays and turn the ignition on. Check for power at terminal 30 an terminal 86 of the relay block with the ignition ON. Fix any wiring faults found.

If the fan operates only on high speed and no electrical faults have been found up to this point, use an ohmmeter to check that the fan resistor is not electrically open.

Window defroster and aux fan are completely different things. The windows defroster uses the blower fan and not the auxiliary fan.
In case your AC does not come on at all, first check the filling of the gas, if too low, AC will not come on, as there is a low and high limit switch.

Last summer I had a problem that my aux fan was not running at all. Checked the 2 relays, then jumpered the connector etc pp., in the end it turned out that the plug pins on the aux fan connector were oxidized, sprayed the connector pins with contact enhancer and all worked again.
On my wrenching buddy's B12 the same problem, there I sprayed the contacts of the low and high relays and their sockets with Stabilant22 contact enhancer and the problem was solved.


Basic problem - dirty pins
Stabilant 22A Electrical Contact Enhancer
Model: All BMW
Complaint:
Connectors which carry low current are more likely to form deposits which affect the resistance of the circuit through the plug connector. Depending upon the particular circuit these deposits can cause malfunctions and consequently activate warning lamps and check control indicators.
Remedy:
Part replacement can temporarily stop the problem.
If the connector is the problem then without disconnecting the connector measure the resistance of the circuit running through the connector to make sure the connector has a high resistance. A good resistor will have close to 0 ohms resistance.
Visually examine the male and female terminals in the connector housing by removing them. Look at the integrity of the wire crimps, and in some male terminals the integrity of the weld of the male pin to the terminal. Then reinstall.
With a zero residue electrical contact cleaner liberally spray the male and female connectors, and allow the air to dry.
Apply Stabilant 22A to both male and female terminals so they are saturated, and reconnect the connectors while they are still wet. When the Stabilant 22A dries it will leave a thin coating of polymer film which is conductive between mating surfaces, and is non-conductive between adjacent pins. It can also prevent the formation of more harmful deposits.

[marvinstockman]

First, I assume the AC was working this summer?

Second, when it's cold outside, the R134 pressure may not be great enough for the system to come on, that is, until the engine kind of heats everything up and raises system pressure. You could be a little low on R134.

Drive around for a bit, and with the car warm, check for AC operation. If you have a set of gauges, check the pressure.

[Chokingdogs]

Well I did some cursory testing...

Aux fan works, both speeds, when jumping the terminals on the rad sensor connector. That, I assume, rules out the fan itself and the relays in the fuse box as being a problem. On a warm day I cycled the AC and the fan/compressor kicked on. When I cycled defrost, the fan did NOT kick on nor did the compressor. Car had been driven for a while so engine bay and engine were up to temps. I still think when defrost is on, the compressor and fan should also kick on. ??

I let the car idle in the driveway for a while to see what happens, and this is what did - temp gauge hit normal, middle, for a while, then crept up to just under the 3/4 line. Without aux fan kicking on the needled just dropped back to normal position. Wasn't a slow drop, pretty quick, two drops w/i a couple seconds or so.

Two questions - what would be an easy way to test the sensor to see if that is operating properly? Second, that quick drop in temps with nothing happening, sound like a sticking t-stat?

When I did the FDM all parts were new, but the sensor was not a genuine BMW part, and I cannot remember where I got it. Was a kit from somewhere, Bimmerworld, etc...The basic kit with T-stat, sensor, etc.

I never had an issue with temps all last summer, and I could tell when the AUX fan would kick on.

[LockDots]

Get a cheap (less than $20) OBD2 Bluetooth adapter and download an app like Torque to monitor the temperature instead of relying on the needle that's super buffered.

Sounds like a sticking T-stat.

[RRSperry]

What defroster? The button on the panel is the rear defroster and has nothing to do with the ac. The front defrost is just the air deverter for the front. On my 95, I have to also turn on the ac with defrost.

[LockDots]

What defroster? The button on the panel is the rear defroster and has nothing to do with the ac. The front defrost is just the air deverter for the front. On my 95, I have to also turn on the ac with defrost.

.
I'm not positive, but I believe in E36's with Auto climate controls the AC kicks on automatically when using the windshield button (or whatever it's called). I've seen all my other newer cars do this as well. I believe it's to blow non-moisturized or dry air onto the glass to help pull moisture away from it.

[hokiemiata]

Side note, the little plug on the bottom of the Aux fan is a Royal POS design. If its not properly covered or gets knocked out or otherwise disabled, it is a single point of catastrophic failure due to overheating. I took out the fan, clipped the connector and hard wired the fan. I know it is a drastic solution, but it was needed.

[LockDots]

It shouldn't be catastrophic. It's an auxiliary fan, not primary.