Auxiliary fan operation - A/C cooling.
 

The OEM fan failed a few months ago. A quick bumper removal and it was easily replaced. Now it's getting above 90 degrees in ATX. The A/C condenser fan function is not working. Rolling down the windows to let hot air out and driving down a block or two, it starts to cool fast. Once the engine is hot enough, the fan is running. The fan winds down after turning it off. Which probe controls fan activation? Is it the ambient air temp probe? The inside temp probe seems to work. I run it at max cooling of 60 F.

Sounds like you're saying your blower isn't blowing.

FSU failure is almost always the cause.

Also: max cold is never very useful. Start at full auto 74° until it automatically adjusts the fan speed down and bump one degree at a time until you are comfortable.

The full speed fan will make the air temp 5-10° warmer and it will never reach the set temp.

The blower motors front and rear both work. I replaced the final stage resistor while troubleshooting on why it won't go to sleep. Still doesn't. I'm down to repairing or replacing the GM3.
A/C will cool faster if the fan kicked on as soon as the A/C is switch on. I'm starting to wonder if the previous owner didn't know it was not working properly He had the compressor and A/C system serviced. I have not connected my R134 gauges to it yet. I don't want to disturb the valve stems. Good to know max cooling is not super useful. I wait until it starts cooling before hitting the button. I'll use auto cooling instead.

What do you mean by "Probe"?

The DME controls the fan speed. That's why when the fan is bad, the DME is the module that you will check for the error code.

I can't really understand the description of the problem here. For example, "fan"? Is there a problem with one of the fans?

But to try to answer just the quoted thing above, and just in case you're talking about the aux fan since that is in the title, you might find the nearby discussion in the following thread useful.

https://xoutpost.com/1191409-post28.html

That section of the thread focuses on tests to determine whether the aux fan is operating as it should, including a description of how the car controls it.

Does the auxiliary fan kick on when the A/C is turned on (when the engine is cold)? I think the auxiliary fand is only turning once the engine is hot. What input to the DME activates the fan? Does BMW use a low/high pressure switch system? Sorry, I don't know how the A/C system activates on an X5. I want the A/C system to start cooling as soon as it's turned on (engine running).

You can activate the aux fan with INPA and maybe some other more advanced scanners.

What brand aux fan did you install? There are reports of some of the cheaper aftermarket fans failing soon after installation

The DME will kick the fan on at key on to confirm it's functional. If you have somebody else turn on the key you will see the fan turn a bit maybe 1/4 turn.

The AC will engage at engine start if everything is working.

The heater will not engage until the engine reaches some magical temp so it doesn't blow cold air when it's already cold out.

Sounds like you are describing that the air doesn't blow until some time into a drive and that indicates a failure of the FSU or the control hardware. Not likely the blower motor but that is possible.

A 2nd level scanner or laptop with the BMW software will request blower on to test the hardware but from experience, and having my FSU fail a month ago, I would be replacing the FSU.

I'm pretty sure OP meant which temp sensor eg the radiator outlet temp but it's the DME that uses a few different inputs to control the aux fan, but that's a moot point.

If the AC ever comes on the aux fan situation is resolved.

You have command of the BLOWER fan speed. If you hit the up button on fan the little bar graph grows and the speed of the blower will rise accordingly if everything is working correctly.

As mentioned, HEAT won't come on when the engine is cold, so something could be confused thinking you are requesting heat even with the snowflake button pressed, so reading of the various temp sensors can help determine what's going on there.

There is surely a flow chart somewhere showing how the blower is regulated from engine temp in heat mode. It sounds like there is something along that line interfering.

Test it this way; cold start set temp to 74 and auto and ac on. See when does the fan kick on: if when the needle on the fake temp gauge leaves the cold zone, it's very likely as I described above.

Drive until fake temp gauge points straight up (means coolant temp between 65-115c), then turn off the car.

Start the car back up, blower should come on immediately as temp will be in the "operational range".

If the symptoms match the description whatever makes the blower not run when heat is called for and engine is cold is almost surely where the fault lies.

1. The compressor starts immediately, but the aux fan is only used to cool the condensor and the radiator.

2. Yes

3. Cooling starts the minute the compressor is engaged. Depending on the compressor, even though it may be turning, it may not be compressing the refrigerant due to a low charge or due to a bad variable compressor.