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  #1  
Old 09-03-2021, 10:50 PM
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A/C observations

I had to do some work on my A/C this week and found out a few more things about the system. I have a facelift and auto air so I have the compressor with the variable displacement valve. The compressors seem to look identical in the pics but have different part numbers. With the valve working properly it holds the low side to 40 ish PSI so the evaporator should never freeze (mine was prone to freezing because the regulator valve was stuck full on instead of "off" like others have had when they had no A/C.) The system with the variable displacement compressor also has a different evaporator temp sensor which does not touch the evaporator and measures the temp of the air that has already gone through so it can not turn off the compressor if the evaporator gets cold enough to start freezing which makes sense since the evaporator should never freeze and the goal of the variable displacement compressor is to not cycle. However there is an additional part number for an evaporator sensor "kit" which might be an adapter to use the non variable displacement sensor and prevent freezing if the compressor is stuck on full tilt. Just a guess on my part but I was thinking of doing exactly that at one point. It might have been tempting to do the change-up when the compressor was $1200 or the valve was not obtainable but the Nissens compressor seems to be top quality and under $300. The variable displacement valve is not all that easy to get and comes in different pressure settings and it seems that the X5 uses a different part number/pressure than anything else. I ordered the valve anyway since I spent so much time trying to find it and was curious so I might replace it in the old compressor at some point. If anyone has a seen a part number/pressure chart for the variable displacement valves that my be interesting as well.
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Old 09-05-2021, 11:31 AM
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What are the part numbers? My '06 probably has the variable drive. I pushed the R134 temp scale pressure to the higher end. Once the aux fan is running, at levels 1-3 it's very cold. I'm sure it's blowing below the '60 degree setting. I don't use Auto or Max settings. Variable drive is fancy for being more efficient at different RPMs. Higher speeds help remove heat faster. The variable drive changes it's pressure stroke.

The issue I've not tackled yet is the aux fan does not turn until engine is at full operating temp. It can take a few miles before it reaches temp. During that time only speed cools it down fast. If driving in city traffic, those first few minutes can be hot. I want to change the pressure switch. Unfortunately, the system has to be evacuated.
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Old 09-05-2021, 02:31 PM
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The valve part numbers are different and not always listed depending on who makes or supplies it. Also there seems to be a color coding involved, all pretty cryptic for someone who's not in the game. If the aux fan runs when you disconnect the pressure switch and doesn't when the high side pressure comes up then you are probably right by thinking you have a pressure switch problem. Sometimes pressure switches can be replaced without evacuating. The desiccant/drier tube is on the left side of the condenser btw if you're looking to put a new desiccant bag in while you have the system evacuated.
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Old 09-05-2021, 02:53 PM
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Once, I pulled the pressure switch. The aux fan didn't come on. It started to get warm in March. I noticed that fan didn't come on when it was at full operating temp. I finally realized the fan was kaput. Luckily, I had replaced the clutch fan earlier. The new fan works when it's at engine operating temperature. I need to pull the connection again to see it turns on. It definitely does not turn on with A/C command.

You don't have push R134 pressures high like I did. It's hot here compared to Canada. The A/C was redone in the last two years. The previous owner had A/C work listed on his ad. The compressor looks new. I wonder if they pulled a fast one on him and didn't notice the fan was not working. I pushed pressures higher and it's holding so far. A 100 degree day is nothing once the fan is running.
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Old 09-05-2021, 04:59 PM
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If anybody has used the BMW 64116 972 109 evaporator sensor "repair kit" it would be interesting to know if my theory about that is correct.
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Old 09-06-2021, 03:33 PM
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A search has not found any pressure charts for a variable compressor. I can tell you on a 100 degree day, mine gets to knuckle chilling <40F. Even the two lowest setting are ice cold. I have turn vents away. I'll keep looking for a pressure chart.
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  #7  
Old 09-08-2021, 02:31 PM
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The pressure regulator I got from Arctic Air is a MT2280 (CV 75-5106 hand written on the package) 172449 etched onto the valve itself. Artic air doesn't list MT2280 for the X5 but some sellers do so I thought I would get one to check it out. I would still recommend to people replacing the whole compressor though. If you can get the Nissens for under $300 you'll be getting a new clutch, brg. and shaft seal as well and these vehicles are getting up there in age and mileage so probably a better way to go.
The variable compressor (2004-2006) is CV717. One E-bay seller has the valve listed as CV-09. I'm not totally sure how the automatic air comes into play on this, do all facelifts have auto air ?
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Last edited by 80stech; 09-08-2021 at 02:51 PM. Reason: add
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Old 09-08-2021, 05:13 PM
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Quote:
Originally Posted by X5chemist View Post
A search has not found any pressure charts for a variable compressor. I can tell you on a 100 degree day, mine gets to knuckle chilling <40F. Even the two lowest setting are ice cold. I have turn vents away. I'll keep looking for a pressure chart.
A variable rate flow compressor should be able to maintain optimal low side pressure without cycling on and off. It shouldn't change the target pressure.

The issue with standard compressors is that they over-compress the refrigerant and will freeze the evaporator if they run continuously. (I briefly ran my E30 M3 with no evap temp sensor... Vent temps in the low 20s and occasionally even high teens were incredible. Until the evap froze over.) VRF compressors are amble to run continuously at optimum pressures.

Net-net, without seeing a chart, I would expect optimum low side, and for the high side to rise as normal, until the system reaches the capacity limit.
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