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Worn Out Compressor?

piperflyer on Mon July 19, 2010 1:03 PM User is offline

Year: 2004
Make: BMW
Model: X3
Engine Size: 3.0L
Refrigerant Type: 134a
Ambient Temp: 90
Pressure Low: 30
Pressure High: 150
Country of Origin: United States

SUV has a Nippondenso 7SBU16C compressor. BMW P/N 64526936883

System leaked out last September. It was a leaky evaporater, I recently R&R'ed the defective part. Also replaced the receiver/dryer since the system was leaked down and at ambient for 9 months. I did not replace the TXV as I had replaced it with an OEM one 2 years ago when I fixed the originial evap leak. (yes, my second OEM evap in 2 years) This time I added 5 oz of PAG 46 into the receiver dryer intake from the condensor. This was to make up for the oil lost from component R&R's. (5 oz was my best guess on amount based on "rule of thumb" advice I could find on-line. Figure better to have a bit more, than not enough)

Vacuum system for ~10 min. Close valves, no movement in low side gauge for 15 minutes. Vacuum for ~50 minutes to dry out system. Car off. Connected 12oz can 134a, purge line, open high side valve to let gas in, check for movement on low side gauge to prove no blockages. Low side starts coming up so close high side, open low side and let system equalize with the can.

Start car, blower on high in recirculation mode, box fan blowing on condensor, turn on A/C to finish charging. Could only get about 8 oz (a guess - it was less than one 12 oz can) into the system. Low side started getting up to ~70 psi with the can connected, would suck down to ~30 psi with the low side valve closed. It was getting very hot in the engine compartment, no cooling from the evap so my guess is the high ambient temps were causing the incresed low side readings. (line from evap to compressor was hot) High side topped out around 140-150 psi.

What I wonder are:
1) Could I have prematurely wore out the compressor due to not adding oil when I first changed out the evap, receiver dryer and TXV? Last time I filled from a 30 lb cylinder. It ran fine for 2 years before this last leak developed. When I opened the sytem this time, the TXV was clean, hence I did not replace it as it was only 2-years old so I assume it is working properly.
2) Could it be that due to the slow charging rate the system couldn't develop enough cooling to overcome the increasing temperaure of the lines?

When I had the system leaked checekd at a local shop, he did a complete fill and said the sytem was cooling fine.

So I'm wondering, was this latest problem because of a weak compressor, or from trying to charge from 12 oz cans? Something else?


Chick on Mon July 19, 2010 2:13 PM User is offlineView users profile

If I understand you correctly you only have 8 oz of refrigerant in the system? You need to get the full system charge into the system before you can trouble shoot..even if that means bringing it to a shop that can get it in by machine...

Email: Chick


Freedoms just another word for nothing left to lose

piperflyer on Mon July 19, 2010 7:02 PM User is offline


Additionally...thinking about my problem throughout the day, if the compressor was producing 140-150 on the high side with only 8 oz (guesstimate) of refridgerant, it certainly was pumping. Perhaps the reason for the elevated low side reading was at only 140-150 psi on the high side, the condensor couldn't transfer any heat out of the refridgerant. The refridgerant simply cycled through the system getting warmer and warmer.

Wish the A/C would quit fighting me. Shoot, I even got an "A" in my thermodynamics classes. LOL. (yes, I know book smarts does NOT mean you know how to turn wrenches - but I'm a descnent wrench...just slow!)

I drop the car off Thursday morning. Let the mechanic with the correct equipment do a full and accurate charge.


piperflyer on Fri July 23, 2010 12:55 PM User is offline

Follow up to close the loop on this topic:

The local shop (independant, not BMW) successfully charged the system with the correct amount of refridgerant. I haven't measure the temp myself but the shop guy said he was getting ~40F (sounds a bit low/optomistic) out of the center air vent when the ambient conditions are ~90F and 65%+ RH. (also not sure fan speed) It definitely was cool enough. I don't know what the low and high side pressure numbers are, but the A/C system is obviously working fine now. Hopefully this latest evaporator is solid and doesn't leak like the last one.

Edited: Fri July 23, 2010 at 12:59 PM by piperflyer

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