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-   -   A/C diagnostics, lots of info w/pics (http://forum.e46fanatics.com/showthread.php?t=881340)

Nervous 10-21-2011 10:40 AM

A/C diagnostics, lots of info w/pics

Maybe you can help me to diagnose what's wrong with my A/C. Symptoms: A/C doesn't engage immediately when ambient temp is about 15-20 C (worked fine during the summer). However, if I drive for about 30 min it finally start to blow cold air (compressor engaged). I decided to check pressure as the first step. I have the following manifold (it is MasterCool 99134-A digital manifold):

My setup:

The reading was the following:
Ambient temp (according to the value on a dash board): 15C (59F), a bit cold for this kind of work, isn't it?
Low side pressure: 30 psi
High side pressure: 230 psi

If I understand correctly, both pressures are too high, isn't it? Especially high side. According to the chart from the manifold's manual, at 65F it should be 25-35 psi for low and 135-155 psi for high. My high is 230 psi!

Note, this was measured when A/C was turned on full blast (min temp, max blower). Our e46s have variable displacement compressors, which are able to change pressure in runtime. Once I increased the temp settings and decreased the blower my readings have significantly changed: 30 psi / 178 psi.
Now they look "more normal", aren't they?

Nervous 10-21-2011 10:43 AM

Update: confirmation that the pressures I see are pretty much in BMW's specs, according to TIS:


The following values apply as normal pressure ranges for ambient temperatures between + 20 C and + 40 C:
Inlet pressure: 1.0 - 2.2 bar
Outlet pressure: 12 - 22 bar

Nervous 10-21-2011 11:08 AM

Another update. Today morning I started the car, turned on A/C (pressed the snow flakes button), set the coolest temp on it, maximum blower speed, and A/C compressor doesn't engage again.
Actually, after reading a lot about BMW's A/C system, my suspect was evaporator temperature sensor. If it fails, the default value for it will be 0C (32F), at this temperature A/C compressor would not engage. It is located somewhere in left footwell. I tried to heat up that place by heat gun with no success.

Ok, I hooked up INPA and read the errors. No errors stored in IHKA module.
But I found out that INPA can tell you a lot about your A/C. For example, it can show you readings from all the sensors, including the evap temp one. Here is the screenshot while A/C compressor is still not engaged (but snow flakes button is pressed):

As you can see, the reading from the evap temperature sensor is correct, but! The pressure sensor shows NEGATIVE pressure!

After sometime, when engine warmed up (after about 20 minutes), the pressure started to grow, slowly at first, reached + 0.5 (compressor is still off) and then faster and faster and at about 5.0 - 7.0 the compressor finally engaged and then the pressure growth stopped at 11:

I have yet to locate the pressure sensor, plus, I forgot to check the value for the sensor when I turn off the A/C compressor (but after it is already functioned) - I'll do it tonight. After I locate the sensor I'll try to play with it (disconnect/connect, cleanup contacts, heat up with a heat gun, etc). However, it might be a blockage somewhere. What if I connect the A/C gauges when compressor is off, can I use the values of the high side to make sure that there is pressure there? (it actually shows about 150 psi when A/C is off, but I need to measure this again BEFORE the A/C compressor started to work).

Any input is welcomed!

Nervous 10-22-2011 08:20 PM

No one, huh?
Nevertheless - an update. Pressure when A/C is off may be around 3 - 5 bar. I also located the pressure sensor, it is on top off the dryer/receiver that is under the passenger side headlamp. I performed a following test: when the car is completely cold and A/C compressor can't engage (INPA pressure sensor value is -1.8 bar) I heated the sensor by a heat gun and the value of the pressure started to grow. Once it reached 1.8 (after about 5 minutes), A/C compressor engaged. Here is the setup:

fotsir 10-22-2011 09:05 PM

Outside temp sensor can cause A/C to not come on for some BMW's; I can't recall for sure if it affects E46 but is your outside temp sensor working okay?

Also, check your coolant level. Another thing I'm not sure of but on some cars the A/C is disallowed unless the coolant is at an okay level.

That negative pressure is odd. Don't forget that it might be a wiring issue.

Nervous 10-22-2011 09:10 PM

Have you read the topic? Yes, my outside temp sensor is fine and as far as I know it is not used as an input value for A/C in E46 (see screenshots of input values above, but not sure, maybe it is; anyway it is fine).
Coolant level is also fine.
A/C doesn't engage when electric fan failed - this is for sure (I had this situation; however, not applicable to the current situation).

Nervous 10-25-2011 11:00 AM

Continuing my A/C challenge.
All of the above actually may indicate that pressure sensor is indeed faulty. The good thing is that it costs just $42 at www.rmeuropean.com and can be replaced w/o evacuating refrigerant (there is a valve similar to high/low pressure valves for connecting gauges). However, here is what worries me: when the A/C system is completely off (engine is running), I must see equals low and high pressures on gauges, correct? This wasn't so when I did check the pressures, even though A/C was off I saw something like 50 psi on low side and 150 psi on high side. I am going to redo this test by connecting gauges to completely cold and not running car to see if these pressures are still different or not. After that I'll heat up the dryer/sensor to start the compressor, wait for some time to stabilize and turn off the A/C. Measure pressures. If they are different now....
What can this mean, especially in conjunction with pressure sensor readings in INPA? Blockage in the dryer/receiver, this is what comes first in my head. So, here what possibly happens:
1) there is a blockage in the dryer, that leads to higher high side pressure
2) this blockage is located AFTER the high pressure port but BEFORE the pressure sensor (either in the pipe or most likely in the dryer)
3) therefore, the pressure sensor may be perfectly fine: there is really no pressure at that point because of blockage.
4) after I heat up the dryer the blockage becomes smaller, it allows some refrigerant to go through. Not completely though, since after turning off the A/C I don't see equal pressures (will verify again, though). Also, not sure how precise should be the reading from the sensor in INPA, but it shows 11 bar utmost, whenever my gauge shows 230 psi (around 16 bar).

Nervous 10-26-2011 10:57 PM

I checked pressures when engine is off for 2 hours. In theory, they should be equal. Here what I saw:

Not equal, 84 psi vs 137 psi. And it was slowly changing: low side was growing, high side was falling. But very slowly, around 1 psi in 2 min.

Is it abnormal? I am leaning to the obstruction theory (in condenser, dryer or expansion valve) rather than faulty pressure sensor. I'll check pressures tomorrow morning before starting the car too. Stay tuned (and chime in!).

shall36 10-27-2011 07:30 AM

Trash in the expansion valve.

Nervous 10-27-2011 10:07 AM

It is a possibility. However, I think the problem is at least complex. Today morning, completely cold car - both high and low pressures are 70 psi. Connected INPA - pressure sensor shows -0.8 bar. I don't see how the pressure sensor may show NEGATIVE pressure, having both high and low at 70 psi. Unless both expansion valve and condenser are clogged, but it is unlikely and if I heat up the pressure sensor I get perfectly cold air and compressor works just fine with no extra sounds or weirdnesses.
So, I think I am going to start with replacing the pressure sensor anyway.

But. I still don't get why equalization of pressures takes so long. Can anybody confirm that high and low pressures should quickly equalize after A/C is off? Please? If yes, when I definitely looking to replacement of dryer, expansion valve and maybe condenser.... But will see what I get after pressure sensor replacement first.

shall36 10-27-2011 12:24 PM

I think you got two problems....one with the pressure sensor and one with trash in the system and/or stuck expansion valve.

System should equalize in about 10 minutes or so...give or take.

Nervous 10-27-2011 12:39 PM

Thanks, shall36, that what I thought as well. I think, condenser may be a suspect too, but I don't see how to prove/ disprove this. The high side charging inlet valve is located BEFORE the condenser and the low side one is AFTER the expansion valve.... Surprisingly, the AC is ice cold once compressor engages.... Ah! Here is an idea: I replace the pressure sensor (located between condenser and expansion valve) first and will compare its value vs the pressures at high side charging inlet. At this point, there is a difference in about 5 bar between them, but I can't trust the pressure sensor at the moment. If I replace it and there is still a big difference in values - then it can be a condenser as well.
If I am going to replace a condenser, I'll anyway replace the dryer and the expansion valve. But if the issue is not in condenser, I'd better replace just the dryer and the expansion valve only.

Nervous 06-20-2012 12:39 PM

Ok, some updates. Due to manual tranny swap I postponed the A/C stuff and now I am coming back to it. I decided to do full A/C overhaul and started from disassembling the A/C system and replacing the expansion valve:


After this I also replaced condenser (since I was replacing radiator anyway and the condenser was a suspect #3 after the expansion valve and pressure sensor). I used an aftermarket condenser (TYC 4994) and I bought it for less than $90 from rockauto.com. Fits perfectly, btw.

Now I've removed the compressor since I want to drain oil from it and replace by new one:

I'll clean it, detach the hoses, drain and refill with PAG 46 oil.
All hoses will be flushed using the A/C flush kit. I'll also replace both schrader valves (high and low pressure). All O-rings will be replaced too.
Next in the list is replacement of dryer and assembling everything back. Vacuum pump is ready to evacuate and re-charge the A/C system, stay tuned.

AUSS1E 06-20-2012 04:13 PM

I am very interested in this cause I have a similar issue. Best I can describe is it is intermittent at best. Not a freon issue, not a compressor issue (It turns even when there is no cold air). I am suspecting the ac control panel or pressure sensor. It seems like when it is really hot and the car sits outside it just wont work. I did evacuate the system and clean out the compressor safety valve and filter, it was quite contaminated. So I also think I may have a condenser issue too.

AUSS1E 06-20-2012 04:21 PM

Also I had talked with a guy who said his HP hose had an internal collapse and that was causing his AC to not work.

Nervous 06-20-2012 04:38 PM

Well, if pressure sensor is bad then compressor does not engage at all. That was an issue with my A/C system and I proved it via INPA (see screenshots above). My second problem was high and low pressures did not equalize quickly enough when compressor is off. That is why I decided to take whole system apart and replace expansion valve, condenser, dryer and flush all the hoses (so, I'll check the hoses during flushing).
If compressor kicks then most likely the pressure sensor is fine. You need to hook A/C gauges to check high and low pressures during the compressor cycles. It might be just low refrigerant issue, or it might be a clog somewhere.

AUSS1E 06-20-2012 04:47 PM

I have gauges and had them hooked up and it is pretty much the same as yours. 30LP and 250HP. It does take a while to equalize but I think after about 2 hrs it is equal. I have watched my gauges as I rev the engine to 3k and the HP works about like a tach. It increases up to about 350 and then slowly comes back down to 225ish. I have checked the gauges when it is not blowing cold but the compressor is running and they indicate low freon 35LP/150HP. But then 30min later it works and blows 30*F air.

I think I may be headed down the same road as you and replace a bunch of stuff. Since you have it all open why not just replace the compressor too?

Nervous 06-20-2012 05:12 PM

Maybe it is ok that pressures equalize slowly then? I'll see once I assemble everything back. (however, in my cases it didn't equalize even after 2 hours). Your numbers look good, meaning that compressor is most likely fine and refrigerant level is fine too. If you have INPA it would be interesting to see screenshots like mine above (captured when compressor is on but no cold air).

Have you checked the water valve, btw? http://realoem.com/bmw/showparts.do?...22&hg=64&fg=18 part #4. A bad water valve may cause air to become warm with A/C on. It is located in the engine compartment, on driver's side. Touch the hose #5 when A/C is on and no cold air is coming out: if it is hot then you've found you problem.

AUSS1E 06-20-2012 05:36 PM

I just replace the heater valve. I dont have INPA. I have the old 1.3.6 scanner but it is very limited.

icm3 07-09-2012 10:48 AM

Did you ever find out if you need to evacuate the system to replace the pressure sensor? Mine is showing a negative "bar" value as well.


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