A/C diagnostics, lots of info w/pics

Yes, I know this for sure now. You need to evacuate the system, there is no schrader valve there (at least not in 2001 330ci).

Thanks for the info! I hope this switch is the issue. Tired of having no A/C and wasting time on it. The negative pressure reading seems odd. It's about -1.8 bar and never changes.

Try to heat up the switch with a heat gun.

I'll give that a try tonight. It would be nice to see my compressor kick on again. I originally went to a local shop to get the A/C recharged because I figured it was low. No dice. Then went to the the local bmw indy (who I'm now certain is out of his element on newer bmw's) and wasted $360 for him to tell me that he couldn't fix it (and told me to take it to the dealeR). He told me that he thinks something is back feeding the A/C relay. I'm certain he didn't check the pressure value coming from this sensor. I think I'll replace the dryer as well.

Update.
I am almost done with assembling my AC system back. I flushed all hoses, condenser and evaporator, unbolted compressor, drained it, filled it with oil (see comment about oil capacity below). Put the compressor back, attached all the hoses, installed inline AC filter. I also have new condenser, expansion valve and drier. Pics to come a bit later.

As to the oil. It is easy to find the right volume of refrigerant (written on a sticker; I wouldn't trust anybody else, such as Bently, if they say something different from the sticker's data). However, the info about oil capacity for the A/C system is very controversial and hard to find. I found the original source of that info for those of us who have Denso compressors (mostly 7SB, I think):
DENSO Catalog (contains oil capacities for compressors)

According to it, E46 uses (7SB) 150-170cc of PAG46 oil (5.0 - 5.7 US fl.oz).
I think, all other sources maybe ignored.

I got the sensor pretty hot. The pressure value was at -1.7 and after a few minutes changed to -1.8. Never went in the positive direction. I have a new sensor and dryer on the way. Hopefully that's it. Any thoughts?

Interesting. I'll stay tuned to see what came of your work and what you determined the root cause to be.

Originally Posted by icm3

I got the sensor pretty hot. The pressure value was at -1.7 and after a few minutes changed to -1.8. Never went in the positive direction. I have a new sensor and dryer on the way. Hopefully that's it. Any thoughts?

If you just disconnect the electrical socket from the sensor - what do you see in INPA?
When you get new sensor, try to connect it (without installing into the low pressure tube) - what do you see in INPA?

When I disconnect it shows a value in the 30's. Very odd.

some good info on this thread...thanks OP...seems like you know what your doing.

Originally Posted by icm3

When I disconnect it shows a value in the 30's. Very odd.

Seems ok to me. When you disconnect the sensor then system thinks the pressure is on MAX (open circuit). I think you are on the right track and this is at least one of the reasons why your A/C doesn't work.

However, negative (or close to zero) pressure from the sensor may also indicate a blockage in the A/C system (in lines, dryer, condenser, evaporator or expansion valve). The only way to rule this out is to disconnect all the lines and flush all lines, condenser and evaporator, plus replace expansion valve, dryer and the pressure sensor (actually this is what I am doing, plus I decided to replace condenser too).

Well...I have surprisingly fast and good news! The new pressure sensor (64539181464) shipped in one day from a nearby warehouse and was waiting for me when I ran by home at lunch time. I decided not to wait for the dryer and take it to the original shop that I had recharge the system. They evacuated the refrigerant, popped in the new sensor, vacuumed (since I decided to forgo the dryer) and recharged the system....and I have ice cold air conditioning again! I CANNOT believe the bmw indy wasn't able to figure this out (and charged me for it). A bit furious about it, but onward and upward. Won't be taking my car there again.

Perfect! I am glad my topic was useful! Hopefully, my AC will work too when I finish.

Sensor now reads 7 to 8 bar when car is off and was ranging from 12 to 15 bar when car was running with A/C on. Thanks for all of the info, it was very helpful in the diagnosis.

As to my update. Yesterday, I finally finished assembling and installed an inline a/c filter.
Flushing:

I used Mastercool flush kit and Craftsman pump to create pressure in the bottle. It has a regular bike's shrader valve on top of the bottle, so no need in big air compressor. The pressure I put in the bottle was 100-120psi.

Inline a/c filter from Auto Air Innovations, Inc. (http://www.auto-air-compressor.com/I..._Filter.html):




After I finished assembly, I hooked up digital a/c manifold and Robinair vacuum pump (model 15500):



Opened all valves, turned it on:


I made a video of the pump running:


Ran it for 45 minutes. Shut it off. Went to bed (it was 1 am).
Next day I checked the pressure it was still around 29 in-Hg, no leaks. Next - charging. Stay tuned.

Ok, charging. I needed to charge 740 +- 25g of refrigerant. One can of R134a is usually 12 oz, i.e. 340g. So, I needed 3 cans and I needed only 60-80g from the 3rd can. I found the cheapest R134a in 12oz cans in Walmart for $9.97. Nobody else could beat the price, even online vendors. Thumbs up to Walmart once again!


So, I used my postal scale to make sure cans are empty:


The whole setup:


I started to fill the system with the engine still off and opened both - low and high - valves on gauges. I achieved some initial pressure, enough to engage the compressor:


I closed the high pressure valve on manifold and turned on the car (never charge A/C from HIGH side!), set the A/C on low temp but on MIN blast. Had to shake and turn the can to empty it. And here is the empty can (initial weight 595g, minus 340g equals 255g empty bottle.


Here is the pressure after the first can is in (a/c compressor is engaged at the moment):


To change cans I carefully closed all valves (LOW on manifold and on the can tap), disconnected the empty can, put a new one, opened can tap, opened manifold LOW valve.
The 3rd can - like I said I needed only 60 - 80 g, so I carefully watched the scale and once it became 500g I shut the valve off.


Then I shut off the LOW valve on manifold. Pressure on idle and MIN blast was good, in specs (considering 80F ambient temp):


At that time A/C already was cold.

I connected INPA. Here is a screenshot of sensors data when A/C is OFF (but blower on FULL blast):


I turned on the A/C, still idling:


I pressed the gas pedal and hold RPMs on 3000 for a minute:



SUCCESS! Finally, I got cold A/C!


BTW, I got the answer how quickly should LOW and HIGH pressures equalize when A/C is turned off. 5, 10 minutes utmost now:


If you remember, previously, it didn't equalize even after several hours!

Hey Nervous - what would you say the issue is if the AC doesn't work well at a stop, but works reasonably well while moving (or maybe it's the RPMs being higher)? I had the system evacuated and refilled a couple weeks ago. When I checked the pressures seemed fine (and then the gauges broke so who knows...). Would switching to an electric fan help perhaps (presumably the electric fan can get more air flowing than the pusher fan)?

Also for anyone who uses NCS expert - there's a setting that lets the climate control unit report the desired temperature as 3 degrees lower than what the display shows. This works even for 59 - so the AC works just a little harder trying to get the temperatures down. For those who like it cold, that may be a nice feature.

Definitely, in general case higher RPMs mean better cooling.
To check if this is really an RPM issue: just raise RPMs on neutral while car stands still: is it cooler now? Even better - connect INPA and check params "Evaporator sensor temp" and "Pressure sensor". How do the change when you raise RPMs?

To check if this is your fan (or maybe condenser is full of dead insects and leaves and that is why air flow is poor) - take a floor fan (if you have one), open the hood and direct the fan on the condenser from the front of the car, put it on MAX. Track INPA's params.

Last time I checked the evaporator temp (ambient was about 95), it was at 42° with the blower set to max. Came down to 35ish if I reduced the blower speed. I'll try to do some more diagnostics this weekend

damn bro, you should open up a shop to diagnose/fix A/C problems with all the knowledge and tools you have now!