AC blower stops and after awhile starts again.

[e28ranch]

Do you guys think it is the air conditioning blower motor resistor in the evaporator box that is not working properly?

Or, could it be the condenser fan relay?

Are there any other relays that it could be?

I did do a search and could not find the answer.

[ahab]

Does the snowflake go out when the blower stops? How's the fuse?

[e28ranch]

Thanks for you help.

The fuse is good and firm in place but I will have to wait until it happens again to find out about the snowflake light.

I just tried the AC again today and it works fine with the snowflake light on. The AC blower always works excellent when the car is cold but after fifteen or twenty minutes, sometimes it turns off. On a cooler day it works longer and does not turn off.

The last time I was driving the AC blower turned off and came back on after about fifteen minutes and then worked excellent for about ten minutes until I got home.

Also, the vent blower motor stops working at the same time that the AC blower motor stops. When the AC motor starts working again, the vent motor starts working again.

[Ohmess]

I have a very similar problem. My A/C evaporative fan just cuts off, and then restarts by itself after a few minutes. Once it cuts off, it will not operate in any of the fan positions.

Attempting to address this, I removed the A/C switch and checked it. I had high resistance between terminals 3 and 5. I cleaned up and adjusted the contacts. Continuity is great now. I also pulled the console, oiled the evaporator fan shaft at the motor housing and ran a straight 12v to the evaporator fan to test it. It ran smooth and quiet.

A/C was strong initially after doing this, but then the evaporator fan shut off. As before, it later came back on without me doing anything (other than opening the windows). Again, the fan will not operate in any of the three speed positions once it shuts down.

I thought about e28ranch’s A/C blower resistor, but I thought when the blower resistor safety switch kicked in the fan could still be operated at high speed. Mine doesn’t do this.

Help!

[gadget73]

is there a thermal cutout in the motor or in/around the speed resistor? that would exhibit similar symptoms, including the "comes back on after a while" part. I claim zero familiarity with BMW stuff but I've seen this in other blower motors. Some of them even have a little rubber hose from the blower housing going into the motor for cooling, if that hose is off the motor overheats. Same if the blower resistor isn't in the air stream. Sometimes those thermal switches get funny and trip when they shouldn't too.

If you can wire a test light across the motor power leads to verify if its still getting power when it quits running that would confirm which direction to check in. If the light goes out the problem is upstream of the motor, if the light stays on when the motor stops, its in the motor.

[Ohmess]

There is no thermal cut out on the motor. The blower resistors have a safety switch, but when that switch is triggered the fan is supposed to operate at full speed. Mine doesn't operate at any speed.

[gadget73]

so much for the obvious then

only thing I can suggest is checking for power and ground at the motor when it quits and use that to determine which direction to chase the problem. Somewhere its losing one or the other if the motor itself isn't the problem.

[Ohmess]

Still wordking on this. I don't think my issue is connected to the compressor diode because the evap. fan fluctuation/stopage occurs even when the compressor is operating. Indeed, it sometime happens shortly after the car is started while the compressor is building pressure. So, it doesn't appear that the cycling of the compressor is causing my issue.

A/C is cold and strong when the evap fan is functioning.

I think I'm going to pull the console and look at the wiring in detail.

[Mike W.]

Also, the vent blower motor stops working at the same time that the AC blower motor stops. When the AC motor starts working again, the vent motor starts working again.

That is very significant. It eliminates the blower motor itself for one thing, and narrows it down to things in common between the two motors.

[ahab]

There's a large relay/control component (for lack of a better term) to the left of and behind the radio. I used to be more versed in its function years ago but I'm too lazy to go digging, so far. Definitely related to temp/pressure and how the system operates. If you drop the kick panel you may be able to smack it when the fan cuts out to see if there's any effect. I can hear the one in my ETA clicking abnormally lately. It almost sounds like there's a squeak in the column when turning the wheel but I'm pretty sure it's a relay fluttering. So far it doesn't affect the AC operation, and maybe it's a symptom rather than a cause, but it's something else you can investigate.

[Federico]

There's a large relay/control component (for lack of a better term) to the left of and behind the radio. I used to be more versed in its function years ago but I'm too lazy to go digging, so far. Definitely related to temp/pressure and how the system operates. If you drop the kick panel you may be able to smack it when the fan cuts out to see if there's any effect. I can hear the one in my ETA clicking abnormally lately. It almost sounds like there's a squeak in the column when turning the wheel but I'm pretty sure it's a relay fluttering. So far it doesn't affect the AC operation, and maybe it's a symptom rather than a cause, but it's something else you can investigate.

That's the Evaporator Temperature Regulator aka the compressor relay. It only controls the compressor based on 2 inputs: the evaporator temp sensor and a signal from the temp knob.

[Ohmess]

Also, the vent blower motor stops working at the same time that the AC blower motor stops. When the AC motor starts working again, the vent motor starts working again.

That is very significant. It eliminates the blower motor itself for one thing, and narrows it down to things in common between the two motors.

It would help me if e28ranch would clarify what is happening here. In my car, when the A/C is switched on, only the blower motor works. So, when my system mysteriously stops by itself, the fan shuts off. However, if I turn off my A/C switch, the heater blower motor operates normally. As I understand the circuit, the A/C switch puts power to only one of the two motors at a time. So, it looks to me like the two circuits are separate with power going from one or the other depending on the position of the A/C switch.

e28ranch - can you clarify whether your heater blower works with the A/C switch off when the A/C blower is not working?

[Mike W.]

Without writing a book (but I may be close) I'll try to distill it down. I've got an advantage here, both that electricity comes easy to me and has always made sense, and I'm not frustrated because I'm not the one without A/C. Trust me, that is not a slight to those who feel like they're banging their heads against the wall, just that some things come easier to some people. And believe me, not everything comes easy to me, but electricity does.

First. The A/C selector, aka snowflake switch. It supplies a full 12 volts to either the heater blower, or the A/C blower, but not both at the same time. So for troubleshooting purposes if you can get in there and measure voltage that helps. Heater is easier to check. But if it's got a full 12 V, why isn't it running at max speed? Well, for both, but with different resistor packs, it goes thru them first. According to the ETM, they both have a safety switch that switches them to max speed in case of overload, but that doesn't appear to be the issue here. But after going thru the resistor packs, they go to the blower speed switch. Independent contacts and circuits in both, only sharing a common ground, which like all good German cars is brown. However, if that brown ground wire/circuit is bad, loose, broken, burnt/??? both will have similar problems, because they both go to ground the same way.

Keep this in mind, both blowers get full 12 volts, it's the ground they switch and throw resistors in to vary the speed. And if the ground is open but either motor has power, you will read 12 V from either terminal with a meter. So if you're troubleshooting and scratching your head about why do I have 12V on both sides, that's why, you're reading the voltage after going thru the motor windings but if it's not grounded, it will just pass thru the winding and you'll read about the same thing on either side. Most if not all of this can be performed on the ground side with the engine and ignition off, you would be measuring resistance, not voltage, to ground, thru a couple of switches, the snowflake and blower speed, plus the resistor pack, but going to ground even with the ignition off.

I tried to put a couple of the ETM images together and they're a little small, but hopefully you guys can follow. Right click open in a new tab or the like and it should be still a little small, but not tiny. Or refer to the full one in pages.

[Ohmess]

Mike - thanks a ton for jumping in here. With respect to your common ground comment, I believe I have good continuity to ground based on two things. First, the heater blower fan operates properly with the snowflake switch off. No surging and no random shut offs. Second, I disconnected the connector to the evaporative blower resistor pack and tested continuity to ground from the brown wire pin (#2) to the chassis. Continuity here is excellent.

I also measured voltage where the green/yellow wire goes into the connector for the resistor pack. (This diagram shows the green/yellow wire going directly to the motor. In my car, there is a two pin connector right next to the resistor pack connector that allows the motor to be unplugged separate from the resistor pack connector. The green/yellow wire shown in the diagram is part of the resistor pack connector in my car with White, Brown, Violet and Gray wires. I presume there is a connection between the green/yellow pin on the resistor pack connector and one of the two connectors on the motor connector.) Anyway, I measured 12v at the green/yellow pin with the car off and the snowflake switch on. This goes to zero with the snowflake switch off.

I'm now thinking the motor is the issue. As noted above, I connected 12v from a spare battery directly to the motor and it spins freely and consistently. Are the any other tests I can perform on the motor without removing it from the car? Could I measure resistance and if so, where would I find a reference value? Should I tap into the wires to the motor and measure voltage while its operating?

Not sure where to go next.

[Mike W.]

Mike - thanks a ton for jumping in here. With respect to your common ground comment, I believe I have good continuity to ground based on two things. First, the heater blower fan operates properly with the snowflake switch off. No surging and no random shut offs. Second, I disconnected the connector to the evaporative blower resistor pack and tested continuity to ground from the brown wire pin (#2) to the chassis. Continuity here is excellent.

I also measured voltage where the green/yellow wire goes into the connector for the resistor pack. (This diagram shows the green/yellow wire going directly to the motor. In my car, there is a two pin connector right next to the resistor pack connector that allows the motor to be unplugged separate from the resistor pack connector. The green/yellow wire shown in the diagram is part of the resistor pack connector in my car with White, Brown, Violet and Gray wires. I presume there is a connection between the green/yellow pin on the resistor pack connector and one of the two connectors on the motor connector.) Anyway, I measured 12v at the green/yellow pin with the car off and the snowflake switch on. This goes to zero with the snowflake switch off.

I'm now thinking the motor is the issue. As noted above, I connected 12v from a spare battery directly to the motor and it spins freely and consistently. Are the any other tests I can perform on the motor without removing it from the car? Could I measure resistance and if so, where would I find a reference value? Should I tap into the wires to the motor and measure voltage while its operating?

Not sure where to go next.

This is getting complicated as there are two different people with similar, but not exactly the same problems. But I'll try to address yours now.

Ground still goes thru the blower speed switch, so if there's an issue with that switch, and I'm not saying there is, it doesn't seem to be a high failure item, but if there is an issue with it, it would be on the ground side. You would have 12V at the motor, both sides, but no run as it wouldn't be grounded.

Green/yellow, coming off the snowflake switch, goes directly to the A/C blower motor. The other side, Brown/Bk, is the ground, switched ground by German color coding, and in fact it goes thru the A/C blower resistors AND the blower switch, before going to ground. I know there's not much access, but pulling the blower motor isn't fun either, but try to get in there and on the ground side, run to ground. If it works, and how much can you really test, I know, but if works repeatedly, it suggests it's a control issue, not the motor. I don't see a location in your sig, where are you, upstate Minn or the surface of the sun in Phoenix. That can help give an idea of how many miles the blower motor has on it. But this line, "As noted above, I connected 12v from a spare battery directly to the motor and it spins freely and consistently. " strongly suggests it's not the blower, rather the controls.

[Ohmess]

Car was originally sold in Fairfax, VA and spent 20 years in and around Washington, DC. A/C would be used three months of the year there. Car was relocated to Aiken, SC 15 years ago, where A/C usage would be a little higher, maybe four months of the year. I bought the car from the original owner's widow earlier this year when the car had 168,000 miles on it.

A/C has been serviced several times and converted to R134. In 2006, evaporator, expansion valve and drier were replaced, but the part number for the evaporator indicates that the fan was not part of the replacement (there is a different part number for the entire evaporator/fan assembly). So, the fan is 35 years old and has been used a lot.

Will try the wire to ground test on the motor today.

[Ohmess]

Evaporator fan is the problem.

After going through the ground side, testing the switch again, testing the resistor pack, testing the fan selector switch and checking the power connection, I was preparing to run a direct ground to the fan, but decided to redo the fan test. This time, unlike my first test, the fan at first did not run, then it ran slowly, then it ran flat out, then it stopped, then it started slowly again. Test was conducted with the fan wired directly to a spare battery, with none of the control circuitry.

Problem is the fan. I'm hoping I can replace the brushes and lube the bearings, but we'll see once I get it out of the car.

My suggestion to e28ranch is to test the fan separate from the car's circuitry. Thanks a ton Mike for your help.