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  #1  
Old 05-14-2020, 12:08 AM
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AC failure diag help

Hello E53 faithful,




This weekend was the first time I've used the AC this year, and it didn't work. My better half has used it already a few weeks ago, but she didn't say anything about it, so I don't know if it was working or if it just wasn't hot enough to tell, or if she didn't notice or what. But it didn't work at all for me. (The car is a 2003 3.0-liter with the manual gearbox. We are in year 4 of ownership at about 111,000 miles and have never had a problem with the HVAC before, even when towing our trailer in hot weather blasting the AC for hours.)

Just before I took the car out, I reinstalled the radiator fan which I had left off since I did the alternator back in January. It is very cold in the winter here so I just thought I would fiddle with it. But when I put it back on, there's the chance that I might have yanked a cable or sensor out, even though I didn't notice it.




Diag steps I've taken so far:

1. I unfortunately cannot get my PA soft to work right now. It was working, now it isn't, and I checked the USB drivers and verified that it is talking to the serial adapter, but not to the car. I checked all of the diag fuses as recommended in another thread. Still doesn't work.

2. I checked for OBDII codes, and there are no current or pending codes.

3. I started the car in the garage and turned the AC switch on and off. While the idle did go up and down a very slight amount when I turned it on and off, I visually verified that the compressor did not engage.

4. The electric fan on the front of the radiator did not turn on at any time.

5. I used this excuse to spend my car budget for the month on a Bentley manual, which gives me the following steps that I haven't already ruled out:

5(a): Refrigerant charge too low or too high. Test pressure.

5(b): Pressure switch faulty. Test and replace if necessary.





I'd like to perform both of these tests. Firstly, I've never checked AC pressure before on any car. What is the easiest way to go about this?



Second, if I check the pressure switch is it just an opened/closed switch, or do I need to be checking impedance or voltage across it? The Bentley manual does not say any specification for this switch, or how to test it.



Third -- anything I'm missing? Any other suggestions? Do I need a Foxwell, INPA, etc to properly diagnose this issue? Thank you in advance for reading and any help.
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  #2  
Old 05-14-2020, 02:00 AM
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AC failure diag help

The low pressure switch is right near the compressor on the suction line maybe within 1' of the compressor. The connector is almost straight up vertixal.

Mine came loose and was entirely why my AC wasn't working so without diagnostic software that will feedback specifics like state of that sensor, pulling It off and measure the residence of the sensor. Manual will say if it is open or short = good but I'm betting on short = good.

If you can figure out how to disconnect the control wire to the clutch you can direct feed power to engage the clutch. (Donít keep it engaged until you know you have pressure).

To test pressure you can buy a cheap refill kit with the pressure gauge and get a basic idea of how much pressure.

I donít recommend adding 134 until you have a better idea of full state of affairs but $15 or $20 will get you a can of 134 and a gauge for the low pressure side which is a decent place to start.

Have somebody else start your car and watch the aux fan. It should move a little bit like 1/4 a turn or something. If it doesn't the fan may not be operational and I've heard that will interfere with HVAC.

I would definitely get a foxwell nt510/520.
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  #3  
Old 05-14-2020, 09:06 AM
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Quote:
Originally Posted by Bdc101 View Post
Hello E53 faithful,




This weekend was the first time I've used the AC this year, and it didn't work. My better half has used it already a few weeks ago, but she didn't say anything about it, so I don't know if it was working or if it just wasn't hot enough to tell, or if she didn't notice or what. But it didn't work at all for me. (The car is a 2003 3.0-liter with the manual gearbox. We are in year 4 of ownership at about 111,000 miles and have never had a problem with the HVAC before, even when towing our trailer in hot weather blasting the AC for hours.)

Just before I took the car out, I reinstalled the radiator fan which I had left off since I did the alternator back in January. It is very cold in the winter here so I just thought I would fiddle with it. But when I put it back on, there's the chance that I might have yanked a cable or sensor out, even though I didn't notice it.




Diag steps I've taken so far:

1. I unfortunately cannot get my PA soft to work right now. It was working, now it isn't, and I checked the USB drivers and verified that it is talking to the serial adapter, but not to the car. I checked all of the diag fuses as recommended in another thread. Still doesn't work.

2. I checked for OBDII codes, and there are no current or pending codes.

3. I started the car in the garage and turned the AC switch on and off. While the idle did go up and down a very slight amount when I turned it on and off, I visually verified that the compressor did not engage.

4. The electric fan on the front of the radiator did not turn on at any time.

5. I used this excuse to spend my car budget for the month on a Bentley manual, which gives me the following steps that I haven't already ruled out:

5(a): Refrigerant charge too low or too high. Test pressure.

5(b): Pressure switch faulty. Test and replace if necessary.





I'd like to perform both of these tests. Firstly, I've never checked AC pressure before on any car. What is the easiest way to go about this?



Second, if I check the pressure switch is it just an opened/closed switch, or do I need to be checking impedance or voltage across it? The Bentley manual does not say any specification for this switch, or how to test it.



Third -- anything I'm missing? Any other suggestions? Do I need a Foxwell, INPA, etc to properly diagnose this issue? Thank you in advance for reading and any help.
Find yourself a mobile mechanic and ask him what it will cost to check the refrigerant pressure in the system. It should only be a 1/2 hour charge. By the time you buy a gauge set and fiddle with how to connect the gauge set to the AC system you are better off letting a tech that has the equipment and knowledge perform this.

Get BMW Scanner 1.4 working and run a diagnostic of the truck. A bad fan will show up in the DME module.
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Old 05-14-2020, 09:10 AM
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Check the pressure switch as Andrew pointed out. It is directly next to the A/C compressor on top of the frame rail. If you simply unplug it with the engine running the aux fan in front of the radiator will run at full speed. There may be a chance your fan isn't working and the A/C will not engage the compressor without the fan working. Just unplug that switch and check your fan first.
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Old 05-14-2020, 09:50 AM
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Thanks all for the quick responses.



I started the car, pulled the plug out of the pressure switch, and nothing changed (with the AC button on or off). I didn't have a second person to help me so I couldn't watch it while the car was starter, but I'll try that later today.



I did double check that the pressure switch was not physically damaged, and the connector was plugged in solidly.



Would this indicate a bad aux fan then? Where does it say that the aux fan has to be running for the AC compressor to start?
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Old 05-14-2020, 10:16 AM
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Quote:
Originally Posted by Bdc101 View Post
Thanks all for the quick responses.



I started the car, pulled the plug out of the pressure switch, and nothing changed (with the AC button on or off). I didn't have a second person to help me so I couldn't watch it while the car was starter, but I'll try that later today.



I did double check that the pressure switch was not physically damaged, and the connector was plugged in solidly.



Would this indicate a bad aux fan then? Where does it say that the aux fan has to be running for the AC compressor to start?
My aux fan failed and my A/C would not engage the compressor clutch. Mine is a 2004 M54 so I cannot be certain other models are the same. Once I replaced my fan, everything worked again. This is where a Foxwell would help as you could simply command the fan to run to check the fan operation. Whether or not this is your entire AC issue, you need that fan in the summer months on the 3.0L M54.
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Old 05-14-2020, 10:24 AM
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Check continuity of the pressure switch while it's unplugged I believe It should be a short.

As to "where does it say" and aux fan required for AC: xoutpost it's the #1 diagnostic mentioned at the beginning of summer when people start to realize their AC not working.

The test I described (watch for the fan self test at start) will let you know the fan is working.

My advice: spend the $ you would ha e on a pro to measure your refrigerant level and buy a foxwell. You'd be able to both contirm status of the low and high pressure cut outs and engage the aux fan and compressor.

I've never had to do the unplug the low pressure sensor test but I didn't remember my fan running constantly for the first two weeks I had my X5 until I realized the low pressure sensor was unplugged so I was surprised to hear that's the usual test method.

So for now and without additional tools that is what you have to work with.

Unplug the low pressure sensor, car running and I'm not sure is ac switch needs to be on, the aux fan is said to kick on immediately if you do this, it's the method commonly used to test the aux fan and I've read often that if the aux fan isn't running the AC will not engage.

The theory is the condenser needs airflow and can't rely on the clutch driven fan when not moving. I have noticed that when I'm stopped and it's warm, if I block the clutch fan the aux fan will kick on in mere seconds so it's very sensitive to temp and kicks in at a much lower temp program when AC is engaged.
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Old 05-14-2020, 11:03 AM
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I had someone start the car while I watched the aux fan. I did not see the blades move at all.



I would think this would be listed in the Bentley manual in the list of possible causes of AC not working, if the fan feedback was truly required for the compressor to be started. But I will take your word for it.



If my PA soft was working, does anybody know if I can try to activate the aux fan or the AC compressor with it? Or do I need to get a Foxwell or similar unit?



In the meantime, later tonight I'll check the pressure switch with my DMM, just to see if I find something out of the ordinary. You are right that if the switch is closed at normal pressure, open at low pressure, then when you pulled the connector off it would think the pressure was low. I'll check that just to make sure there's nothing funny going on with it.


Edit: MY GOD, $600 for an electric fan???
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Old 05-14-2020, 11:19 AM
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It's not so directly said here but DME won't allow compressor activation if there is active code for aux fan which is monitored and PWM cotrolled.

https://www.pss-autosoft.net/diagram...-001645001.htm

https://www.pss-autosoft.net/diagram...SO-6450002.htm
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Old 05-14-2020, 11:51 AM
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Quote:
Originally Posted by Bdc101 View Post

If my PA soft was working, does anybody know if I can try to activate the aux fan or the AC compressor with it? Or do I need to get a Foxwell or similar unit?

Edit: MY GOD, $600 for an electric fan???
PA Soft does not have the functionality to command any process. It is more of a scanner, coding tool.

I paid a little over $200 for my Behr aux fan when I did it 5 years ago. The money isn't that bad but the replacement job requires removing the front bumper.
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