AC failure diag help

upallnight · #1 05-14-2020, 09:06 AM

Quote:

Originally Posted by Bdc101

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.

Overboost · #2 05-14-2020, 09:10 AM

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.