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E36/7 Z3 (1996-2002)
E36/7 Z3 Roadster, Z3 coupe, Z3 M Roadster and Z3 M Coupe talk with our gurus here.

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  #1  
Old 04-01-2014, 08:50 PM
diva_3181377 diva_3181377 is offline
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Location: Dallas
 
Join Date: Apr 2013
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Mein Auto: 2000 Z3 2.5L Auto
What is your AC pressure at idle?

For me when i checked last time,
pressure at 90-95F with 45% humidity in the garage. Before engine start (after running 30 minutes), it was 105 PSI on both side, at idle it was 50 PSI on low and 220 PSI on high. At 1500 rpm it is 32PSI and 265PSI and at 2500 rpm, it is 23 PSI on low and 285 PSI on high

Does it seems low? a weak compressor? At idle, it should be in 30s? The amount of R134a is correct.

I found a used one at http://www.ebay.com/itm/200978685290...S:1123&vxp=mtr. Seems good?
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  #2  
Old 04-02-2014, 04:24 AM
Blacklane Blacklane is offline
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What is the ambient temperature? That matters greatly in testing air conditioners.

Edit:
I've re-read your post. Are you saying that the ambient temperature is 90-95F?

These cars use a variable-displacement compressor. The value at idle is not particularly important. It's the value at 1500 rpm that matters. 32/265 is not too bad, maybe it bit low for the ambient temperature. Maybe you need a tiny bit more refrigerant. Otherwise, I think you're good.

Why do you think it's bad?

Last edited by Blacklane; 04-02-2014 at 05:18 AM.
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  #3  
Old 04-02-2014, 07:34 AM
diva_3181377 diva_3181377 is offline
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Mein Auto: 2000 Z3 2.5L Auto
Well, when the outside was like 80s or low 90s it is working fine. Above that, at idle, it is not cold enough when compared to other cars. Like a vw or honda. The same temperature at same location, the vw showed 30s on low and 250s on idle. Honda was 40 and 250. I saw some posting (not related to z3, but 3 series) saying the low should be in the 30s at idle. I am getting it only at 1500 rpm instead of the 750 idle rpm. That's why i thought the compressor is weak.

Compressor is silent, may be a small whine, that's it. No noise at all.

What is the usual pressures at 1500 rpm? I mean for the same temperature and humidity?
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  #4  
Old 04-02-2014, 06:54 PM
Blacklane Blacklane is offline
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Does the Aux fan in front of the radiator come on when the air conditioner is turned on? If not, that would explain poor performance when the car is not moving.

Regarding your original post about buying a used A/C compressor, I would not do it. There is no reason to think a used part would be better than your existing part, yet could be far worse. For something like a compressor, you should look for rebuilt. RockAuto.com usually has compressors for these cars, usually from several different suppliers at different prices.
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  #5  
Old 04-03-2014, 06:55 AM
diva_3181377 diva_3181377 is offline
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Yes. The Aux fan does come on when the AC is turned on. The AC is cooling, but not enough for the high temperature. Initially had issues with it, the connector was loose. Fixed it and it is good now. Also tested the high speed also (last year when temperature was really high). It was spinning at high speed which is really easy to hear.

Thanks for the tip. I will check RockAuto.com. Never thought of the issue since it is also a wearable item.

It needs 6 Oz of PAG 100 right? Add it to the suction port and rotate couple of times.

Just want to know. What pressures are you seeing at 1500RPM for say 85F? If mine is not really bad, i can live with that? Any advantage in just changing the PAG oil? Since the car is almost 15 yrs old, the oil can dry up?
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  #6  
Old 04-03-2014, 04:26 PM
Blacklane Blacklane is offline
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There is no reason to replace the PAG oil. It does not degrade. The only time to replace it is when the system is open for other maintenance and the oil is lost.

It is bad to add too much oil. That displaces volume needed to expand the refrigerant. Adding 6 oz is way too much, even when replacing the compressor and receiver/dryer. The entire system needs only 4.1 oz.

If you open the system, you should always replace the receiver/dryer.

Is there a chance that you have air in your system, such as the result of using one of those refill kits that have no purge valve? That would be a reason to completely evacuate and refill your system with a known amount of R-134a. (You would not need to add oil at this time either). My experience with variable-displacement compressors is that it is best to fill by weight, not pressures. The required weight is listed on the green sticker under the hood.


Look over this thread: http://www.bimmerfest.com/forums/sho...d.php?t=700607
and this one: http://www.bimmerfest.com/forums/sho...d.php?t=493146
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  #7  
Old 04-03-2014, 06:32 PM
diva_3181377 diva_3181377 is offline
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Mein Auto: 2000 Z3 2.5L Auto
Thanks Blacklane. I was thinking like PAG oil is also like ATF which needs replacing after few years. Good to know that i don't need to replace it.

When i refilled last time, used the weight method. 900 +/- 25gm (on sticker). Used 2 full bottles (2X 340) and then the last one using a digital scale. Vacuumed it first, wait like 30 minutes and then filled. Also replaced the expansion valve and drier (used store brands).

Because i replaced the drier and expansion valve, can it loose some PAG oil in it? I just put the new one without adding any oil in it. Some people says i need to put some in the drier?
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  #8  
Old 04-03-2014, 07:34 PM
Blacklane Blacklane is offline
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Not really. Normally the receiver/dryer does not contain enough oil to worry about. I've cut a few open, and there was virtually no oil at all in them. Most of the oil is in the compressor (maybe 70%), then the condenser (maybe 20%), then the evaporator (maybe 5%), and the remaining 5% in the receiver/dryer and lines. These are gross approximations on my part.

Your system still could be low on refrigerant or you could have a bad compressor. All R134a systems work on the same pressure/temperature relationships (it's straight physics), so you can just search online for "R134a troubleshooting" to find diagnostics manuals to use with your gauges. One of my favorite charts is used by Honda and has the ambient temperature, center vent temperature, high pressure, and suction pressure all on one set of graphs.

Last edited by Blacklane; 04-04-2014 at 04:30 AM.
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  #9  
Old 04-03-2014, 09:35 PM
diva_3181377 diva_3181377 is offline
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Thanks for all the information Blacklane..
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