What cause A/C compressor not engage?

[g300d]

Originally Posted by tr125

That’s what the previous owner told me. but anyway I just came back from a shop, the mechanic charged me $90 for a inspection with recharging the system, but compressor still not engage. He told me that may be there are something wrong with the controls, but did not say anything about the Aux fan. He told me to make an appointment to drop of the truck in order to do further inspections and not able to do any repair estimate yet. So I just wait until this Sat and hopefully I should know what is wrong.

Well, rules out low refrigerant, and since you jumped the clutch and the clutch engaged, thats ok too.

Leaves a lot to check though. From sensors and relays to switches to control unit/s.

Again best to scan it so you and the AC shop have a place to start. Good luck!

[upallnight]

Originally Posted by tr125

That’s what the previous owner told me. but anyway I just came back from a shop, the mechanic charged me $90 for a inspection with recharging the system, but compressor still not engage. He told me that may be there are something wrong with the controls, but did not say anything about the Aux fan. He told me to make an appointment to drop of the truck in order to do further inspections and not able to do any repair estimate yet. So I just wait until this Sat and hopefully I should know what is wrong.

How can a mechanic charge an ac system if the compressor is not engaging? The system needs to be running in order for the tech to observe the low side and high side pressure

If he's just an Indy shop with no diagnostic software for a BMW better off taking the X to a BMW specialist or dealer who has the software to diagnosis the problem. With the correct software, you can command the DME to engage the compressor, turn on the aux fan, see system pressure, etc, etc, etc.

Otherwise he just a shade tree mechanic living in an analog world dealing with digital problems.

[E53inLA]

We had a bad Aux Fan in our 2005 E53. Now I know, if I turn on the AC full blast and the Aux Fan doesn't come on with 30-60 seconds, something is wrong.

The funny thing is I remember when the X5 was new the Aux fan would run for a while after we turned off the engine. When it failed, I just didn't notice that any more. Mechanic told me it's not a well made part and is prone to failure.

[upallnight]

Originally Posted by E53inLA

We had a bad Aux Fan in our 2005 E53. Now I know, if I turn on the AC full blast and the Aux Fan doesn't come on with 30-60 seconds, something is wrong.

The funny thing is I remember when the X5 was new the Aux fan would run for a while after we turned off the engine. When it failed, I just didn't notice that any more. Mechanic told me it's not a well made part and is prone to failure.

It's not that it not a well made part, but a complicated part. Before it was just a DC motor that was switch on and off with a relay, but now the aux fan is controlled by the DME which sends a pulse signal to the circuit board that is built into the motor that interprets the pulse to turn it on and the width of the pulse to determine the speed of the aux fan. The more you make something complicated the more the chances of failure.

[tr125]

Originally Posted by upallnight

How can a mechanic charge an ac system if the compressor is not engaging? The system needs to be running in order for the tech to observe the low side and high side pressure

It looked like he had a diagnose station in front of my truck when he was working on it. I did not know how did he recharge the system. But He did told me that the clutch can be forced to engage. Not sure if he jump it or program it to engage.




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[tr125]

Just did another inspection today. Technician told me that the auxiliary fan has some problems which cause the clutch not to engage. He quote me about $700 to replace the fan. I don't want to span this much now. However my A/C is blowing cold while i was driving home after the inspection, and the Aux fan is working right now. This is weird, but it kinda makes me happy. but not sure when is going to fail again.

[E53inLA]

Originally Posted by upallnight

It's not that it not a well made part, but a complicated part. Before it was just a DC motor that was switch on and off with a relay, but now the aux fan is controlled by the DME which sends a pulse signal to the circuit board that is built into the motor that interprets the pulse to turn it on and the width of the pulse to determine the speed of the aux fan. The more you make something complicated the more the chances of failure.

No argument there. In our case, the AC would not work in city (stop & go) traffic, but would work at constant highway speed.

After the fan was replaced, if I start the motor, turned the AC on max, the fan would start within 30-60 seconds, and the AC would blow cold. This is standing in my driveway.