[E92_William]

There doesn’t seem to be much of a straight answer out there for our cars when it comes to servicing a working system.

BMW gives you information on the amount of R134a/oil if you vacuum and fill an entire system but no low and high line pressure. And obviously no vent temperature relative to outside temp and humidity. The “standard” charts online are all over the place.

I’m servicing two E9x, a 2012 E91 and a 2008 E92. Both cool just not enough.

E91
I was getting this yesterday after adding 6oz
29-30 low
230 high
About 46-47F out the vents
81 ambient 73% humidity


Will be working on that again today (at 90F) but wanted to hear what pressures you guys have gotten and your vent temps relative to ambient. Thanks

[E92_William]

I just tested the E91 again.
35 low
250 high
54-56F out the vents
55% humidity
90F

Can this be improved?

E92 however:
25 low
175 high
Same temps and humidity
82-88F out the vents

Classic low refrigerant case, will update once serviced.

[mainbearing]

At idle or 2000 rpms? The E91 numbers look fine, about where mine are. +1 E92 is low on refrigerant.

A scan tool like INPA can give you evaporator temp. 36-41F is about where evap core should be. And in hot S. FL, a 35F temp drop at the vents looks ok. You can try with windows closed and parked in the shade, and see if vents drop lower after 5-10 minutes.

[marvinstockman]

Your temps will be better when your moving on the road.

Please, please it really seems like you should leave it alone.

Remember, AC is AC, and BMW is just AC.

If you must, go to Youtube and look up troubleshooting with gauges, but as long as it gets cool don't overfill. Remember too little is better than too much. What ever you do, don't make yourself crazy trying to fix something that isn't broken.

[E92_William]

Originally Posted by mainbearing

At idle or 2000 rpms? The E91 numbers look fine, about where mine are. +1 E92 is low on refrigerant.

A scan tool like INPA can give you evaporator temp. 36-41F is about where evap core should be. And in hot S. FL, a 35F temp drop at the vents looks ok. You can try with windows closed and parked in the shade, and see if vents drop lower after 5-10 minutes.

Yes at idle. I drove the e91 around the block a couple of times to get up to temp before measuring but was at idle for a while when testing. When I bought this car last year the AC was a bit more powerful for sure. Unfortunately the newest E9x is now 11 years old so we don’t know what the AC was like when new.

I’ve seen dudes online get a car in a 90 degree garage to put out 40 some at the vents. Maybe it is that im in the driveway but I got with a sunshade on.

These are my numbers on ISTA. Now im at 57-60 out the vents at idle

[E92_William]

Originally Posted by marvinstockman

Your temps will be better when your moving on the road.

Please, please it really seems like you should leave it alone.

Remember, AC is AC, and BMW is just AC.

If you must, go to Youtube and look up troubleshooting with gauges, but as long as it gets cool don't overfill. Remember too little is better than too much. What ever you do, don't make yourself crazy trying to fix something that isn't broken.

I know it seems ridiculous but I’m going after that last 5-15% of performance out of the system. I’m not crazy, this car used to cool better when I got it a year ago so I need it to get to that point. I’ve been doing a lot of research and soaking up as much information as I can so I don’t overservice the system or damage something.

It’s 90 outside and I’m getting 60 out the vents at idle, I know it’s not perfect but I think if I bought this car new in 2012 it wouldn’t have put that measly 60F out the vents.
Pressures are now 36 low and 250 high

[mainbearing]

Your evap is at 11 C and IMO that is too high. It should be 2-5 C. Try taking it to 2000 rpms and see what the pressures look like. Hopefully the high side does not go through the roof. Is the radiator cooling fan working? With mid 80s I can get 50 F. It has been about that since new. Still mediocre but probably is the norm for European junk.

[E92_William]

Originally Posted by mainbearing

Your evap is at 11 C and IMO that is too high. It should be 2-5 C. Try taking it to 2000 rpms and see what the pressures look like. Hopefully the high side does not go through the roof. Is the radiator cooling fan working?

Yes the fan works well. I can’t see the pressures now while revving the engine but I just did that a second ago and this is what it looks like on ISTA at 2000 rpm. Substantial drop to 6-7C but not the 2-5 you mentioned.

[mainbearing]

Also, the 13.6V charging voltage looks a little low. Mine stays around 14.1 or so just about all the time. It might have dropped to 13.9V after a long highway drive but cannot remember for sure.

And your high side went to 18 bar (~260 psi). that sounds a bit high, but maybe not for S FL 90F. When I rev the low is about 30-35 and high is about 220-240 in mid 80's ambient. It's been like that. This year I added 1 oz a few months back.

Use a garden hose and trickle some water over the condenser. See how things improve. If the high side quickly drops then maybe there is some air in the system?

BTW, what was the low side pressure reading when the evap was at 6 C (maybe place the gauge by the strut tower like when I rev)? Vent of 11 C (52 F) is getting there.

[E92_William]

I just got me a test subject to watch the gauges as I rev it.

At 2000 I’m getting:
26-27 low side when the evap is at 6C
High side the gauges say 285 give or take however ISTA measures 18.5 bar to 19 which is 270-275 maybe it’s reading a bit low (harbor freight)

I just tried spraying water for a bit through the grilles. Result was a refrigerant pressure drop from 16.5 (240psi on ISTA) to 11 bar (160psi) . A 1C drop in evap temperature and 1 in footwell and interior aswell. Now it’s holding at around 13 bar (190-200psi) after revving and idling without water and evap holding at 6-7.

Also my battery seems a bit lower but I had been toying with coding out features so not fully charged. Now at 13.8v

[mainbearing]

Come to think of it, the pressure gauge readings seem to be working, so I do not think battery management is messing with the AC compressor.

Evap temp is still high, especially with the low side at 26-27 psi.

I am at a limit of what I know about AC. If you happen to have an IR thermometer, maybe check the condenser to see if there is a rapid temperature chagne. Air would collect on top of the condenser.

Just some guesses: some air in system, slight refrigerant over charge, possible expansion valve problem?? Not really sure tho.

From what little I understand about evaporator superheat, looking on Rockauto expansion valve specs, Four Seasons expansion valve shows -1.5 superheat. The low side return line is hard to get to, but that pipe by the firewall should be about 32-35F with 27-30 psi low gauge, which does not seem to be the case from the evap temp readings.

https://www.rockauto.com/en/moreinfo...PEJ2f4rNCGHJlC

[E92_William]

Originally Posted by mainbearing

Come to think of it, the pressure gauge readings seem to be working, so I do not think battery management is messing with the AC compressor.

Evap temp is still high, especially with the low side at 26-27 psi.

I am at a limit of what I know about AC. If you happen to have an IR thermometer, maybe check the condenser to see if there is a rapid temperature chagne. Air would collect on top of the condenser.

Just some guesses: some air in system, slight refrigerant over charge, possible expansion valve problem?? Not really sure tho.

From what little I understand about evaporator superheat, looking on Rockauto expansion valve specs, Four Seasons expansion valve shows -1.5 superheat. The low side return line is hard to get to, but that pipe by the firewall should be about 32-35F with 27-30 psi low gauge, which does not seem to be the case from the evap temp readings.

https://www.rockauto.com/en/moreinfo...PEJ2f4rNCGHJlC

I’m definitely at a limit of what I know and just now reading up on superheat and sub cooling as I didn’t even know they were a thing. I’ve been watching many videos on it and it seems some cars will have much higher numbers than others.

That -1.5 on the rock auto valve, I figure is in degreees C? I can definitely manage a way to measure these two values but I’d need to know what an ideal one is too.

I don’t think I’ve introduced much regular air into the system, I bled the charge hose before charging 6oz yesterday but I didn’t do the low pressure hose. Maybe that’s enough “air” to cause this? I’d have to keep reading

[mainbearing]

I think the superheat is in degrees F, because I see some expansion valves on Rockauto that are 8 to 10. No way those numbers are C, that would be too much superheat.

I have not performed superheat measurements myself. So just repeating what I think I understood....at a typical 35 psi on the low side, the refrigerant temperature should be 40 F (or 4.4 C. See pressure-temperature chart below). And with an expansion valve of -1.5 F then, the temperature of the pipe out the expansion valve should be 40 - 1.5 = 38.5 F.

If the superheat is higher than specified, then less of the evaporator is flooded with liquid refrigerant, and the cooling will suffer.

Anyway your evaporator is no where near that cold. I do not know why, as there can be many reasons, including heater air leaking into the cold side, etc.

On an expansion valve system, the expansion valve superheat is set at factory, so I do not look at them when things are working. The supercooling of the condenser can be used during charging, but I have never done that either.

When I feel the AC not as cold and see the high side around 200 or below (ambient starting into the mid 80s), then I top up a couple of ounces to bring it to 220-230 for the season. This ghetto method has always worked for me, so I try not to overthink it.

R134a pressure-temperature chart:
https://www.arkema.com/files/live/si...ture-chart.pdf

Originally Posted by E92_William

I’m definitely at a limit of what I know and just now reading up on superheat and sub cooling as I didn’t even know they were a thing. I’ve been watching many videos on it and it seems some cars will have much higher numbers than others.

That -1.5 on the rock auto valve, I figure is in degreees C? I can definitely manage a way to measure these two values but I’d need to know what an ideal one is too.

I don’t think I’ve introduced much regular air into the system, I bled the charge hose before charging 6oz yesterday but I didn’t do the low pressure hose. Maybe that’s enough “air” to cause this? I’d have to keep reading

[Brian86]

My 2cents.....

Vent it, evacuate it, add an oz or two of oil, then refill it to spec.

Osmosis is a funny thing, and despite it not 'leaking' refrigerant systems do acquire air over decades (yes, the nitrogen in the atmosphere actually climbs the pressure gradient through the o-rings)

From a more pragmatic perspective... I've spent weekends doing the same thing with pressure gauges, but could never get it 'just so' like a a vent and refill would after I'd get frustrated.

[mainbearing]

Here is a video on an "accumulator system" that shows how to measure subcooling of the condenser. There are other hvac industry videos I think are similar, but this video is on a car. It is nauseating however has the details of using a pressure-temperature chart on a car so I linked it here.

The superheat of the expansion valve would be similar. Except it is measured on the low side. BMW uses riser pipes with access ports, and those locations by the ports are probably not the best for taking temps, as the temps may be much higher because of the risers.

A shop can evacuate and measure the refrigerant in the system (in case of overcharge they will know). And with the system empty it is a good time to change out the expansion valve if that is the problem. The desiccant bag, on earlier BMWs are replaceable, should be changed as well when a system is opened. In case the lower pressure is caused by ingressed moisture freezing in the expansion valve.

Again, I used the ghetto method of just bring the pressure back to where I knew it was for the ambient and that worked great for me.

Example of one type of E90 desiccant bags:
https://www.rockauto.com/en/moreinfo...=16858&jsn=454

[Tambohamilton]

From what I've heard or figured out;
1. Pressure is a really inaccurate way of filling the system, so be careful. Under-fill instead of over. This is why BMW don't give pressure specs for the system.
2. Battery management doesn't mess with AC at all really, because the AC compressor takes very little electrical power (the blower fan uses a lot more).

[Bims328i]

Quite interesting imo. Not sure if my system has been tampered with but it has sustained quite good performance.

Typically only run it after the car is moving to minimize fan usage but in this FL heat, it's almost unbearable.

To further minimize fan usage from A/C I will almost always utilize recirculation ♻️.

I've said it before, but this is one of the main factors of A/C failure. That is repeated longstanding conditioning of outside air over the life of the vehicle.

Yes, you might want some fresh air in the cabin from time to time but continuously using this while you drive around leads to additional unnecessary condensation build-up on your cooling core which of course increases the chances of corrosion build up.

Using recirculate does not bring in fresh air but it is equivalent to MAX AC setting as it recirculates the already conditioned air which has had the insane mass of Florida humidity removed until you crack a window or disable recirculate feature.

Using this over the long run can help preserve your AC system as you are not trying to always condition the worlds air and not the bit isolated within the cabin which becomes less taxing as it is conditioned. Best regards.

[gbalthrop]

Some Folks make "Topping Up" the Refrigerant in an Auto R-134a system MUCH more difficult than it needs to be. Some of the links in this thread (such as Vapor Pressure at particular Temp) have NOTHING to do with simple addition of R-134a refrigerant.

For instance, see these "Temperature-Pressure Charts" for R-134a refrigerant, ALL of which have SAME High & Low Side pressure readings for a particular Temperature. OP's data was read at ~ 90F, so simply using that Ambient Temp, The LOW side should be 50 PSIG (Gauge Pressure) +/- 5 PSIG, & HIGH Side should be 260 PSIG, +/- 10 PSIG. Compare the three linked charts for R-134a. They are NOT "all over the place". They are the SAME:
https://rechargeac.com/how-to/ac-system-pressure-chart
https://www.autozone.com/diy/climate...echarge-car-ac
https://www.acprocold.com/help-and-a...ressure-chart/

So if your Radiator "E-Fan" is working, simply Connect Manifold gauges & check pressure values. If BOTH Low & High Side pressures are BELOW the Chart values for that Ambient Temp (your E9x shows Ambient Temp on Instrument Cluster), then you need to ADD R-134a. How MUCH you ask?

The Manifold Gauges will tell you "How MUCH". Add Refrigerant SLOWLY, & watch the gauges. Make sure your E-Fan continues to run (air flow through Condenser in front of Radiator), and if in doubt about that airflow, use external Electric Fan to blow air on front of Condenser.

STOP adding Refrigerant when either gauge value gets "in-range". Let system pump refrigerant for a few minutes as you check Evaporator Temp with INPA, ISTA, proper Scan Tool or Thermometer. If you have INPA/ISTA, you can monitor Position of EACH of 8 Flap Motors.

The TWO Most Important ones are Left & Right "Mixed Air Flaps", which are SUPPOSED to Direct NO Air through Heater Core when "MAX" button is pressed, or when in full cooling mode with BOTH T-Stats set to Coldest Temp setting. If Air Temp coming from vents on ONE side Differs from Temp on OTHER side, then you likely have a flap issue.

Keep in mind that a fully-evacuated system takes 20.8 Oz., +/- 0.4 Oz. of Refrigerant. NEVER add more than that. Most DIY Refrigerant Cans are 12 Oz. That 20.8 Oz. value is on the Label under the Hood of my 3/2007 build 328xi. CHECK YOUR LABEL, and if the value differs, please advise.

If you have INPA/ISTA, ALL you need is a charging handle with Gauge to show Low Side Pressure, & INPA/ISTA will show you High Side pressure (probably Absolute Pressure, which is 14.5 PSI MORE than Gauge Pressure or PSIG). Anyone with BOTH Manifold Gauges AND INPA/ISTA, please advise of your comparison between High Side GAUGE PSIG reading vs. INPA/ISTA "bar" reading for "Refrigerant Pressure Sensor" (High side) Value.

Both ISTA & Bentley Manual (based largely on ISTA), state to change Desiccant/ Condenser (depending upon Model Year) if refrigerant system open to atmosphere for MORE than 24 hours. That suggests that you CAN open the system to change components or O-Rings and NOT have to change desiccant, AS LONG AS you seal system with plastic plugs or such while working on it.

IF the system has been open to atmosphere > 24 hours, the Desiccant (moisture absorber) is probably FUBAR, & cooling will suffer without changing Desiccant. Also, if air ("NON-Condensible") has entered system, cooling will suffer. If system has never failed to operate (NO Compressor Valve operation) due to LOW Refrigerant Pressure, it is NOT likely that there is Air in System. However, if you don't know vehicle history, you can only guess.

Refrigeration Oil: If you simply have a slow leak of refrigerant in system > 10 years old, unless you see oily residue at a fitting or leak site, the System has probably NOT lost any Refrigeration (PAG) Oil.

So for most systems that have always worked, but now are cooling LESS than desired at 10+ years of age, simply "Topping Up" Refrigerant, using Manifold Gauge Set (< $35 Amazon) will work for most. Make sure you are getting "Quick-Connect" fittings for R134a Auto Refrigerant System.
George

[E92_William]

Thanks guys, lots of very good information here, I did much research overnight and this morning regarding sub cool and superheat and it seems it is a solid way to diagnose the actual charge of refrigerant doing work in the system instead of just pressures. Which could as listed above, have some air in it due to osmosis or tampering. While vacuuming the system and filling it again would be the best way about this, I really want to try and figure this one out before throwing the towel and doing that. Bit hard to reply to every single comment but taking all into account.

So knowing that and with the videos posted above, I attached two temperature probes one to each port, it seems it depends on the system manufacturer where they want you to take this reading if before the compressor or right after the valve so I did it like the guy in the video.. also wrapped a rag around it to maybe hopefully insulate the readout some and we can adjust for them being hotter than in reality as it’s measured in the riser pipe of the evap.

The numbers are these:
High side
145F saturation at the gauge set for the condenser
123F measured at the port with the probe
This leads to:
23° Subcool if I’m measuring correctly

Low side
40F saturation at the gauge set
80F at the probe
This leads to:
40° Superheat.

That seems like a pretty stark difference. I found this other video showing how to do it and diagnose with the readings. The picture on white paper is a screenshot from it. By what he says I need to add some r134 to the system. As George also pointed out from his charts. I might be on the low end of the pressures for a day in the 90s in Florida.

Here is a small picture spam of probe location and readouts.

[E92_William]

Also decided to check flap position and this is what I noted. 68% on the recirc one. Is that normal on max AC set to recirc? I figure if it wasn’t it would trigger a code as it wouldn’t be as the car requested.

[E92_William]

Assuming that my pressures were lower than they should be according to the charts, I added some more refrigerant and kept track of the superheat and sub cooling measurements. While the evaporator temperature on ISTA can now steadily maintain 8C at idle which is better than before and when revving the engine I can get the evaporator to 4C after a while.

The more refrigerant I added the larger the gap between the subcooling and superheat was. To the point where now the subcooling is about 11-13F and the superheat can go to an staggering 55F. This goes against the common logic that high superheat means low r134 in the system. Also adding refrigerant didn’t significantly impact the pressure readings almost at all.

[mainbearing]

Looking at the 3 charts (post 18), those are for refrigerant cans with a low side gauge and are for "accumulator systems". If an expansion valve system is charged to 45-55 psi low side, then the system is way overcharged.

Looking at OP's numbers, I think 40 def F superheat is way too much. That tells me anyway the evaporator is starved of liquid refrigerant. I would try to find the coldest spot on the low side pipe near the expansion valve and double check.

There are no specs for supercool on the condenser side, but hvac industry looks for something like 10 F. On the condenser side 23 F supercool I would say is ok and probably slightly high (as well as the pressure).

OP can try running this setup for a while if the evap is down to 4 F (is that at idle?). My concern would be at higher rpms the high side might go through the roof and cause pressure relief of the refrigerant.

I do not know about flap position readings. I wonder if clamping off a heater hose can help test hot air leaks into the cold side.

Just want to make sure, you are measuring superheat temperature on the bigger pipe coming out of the expansion valve correct? If the subcooling decreased on the high side and if the low side temperature probe is on the >>liquid line<<, that would explain the higher "superheat" next to the expansion valve by roughly the same amount.

Also, is there frost on or near the expansion valve?

Additional info video: