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  #1  
Old 04-26-2009, 04:44 PM
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E320 a/c problem

I have a '99 E320.
The passenger side A/C blows cold but the driver side has no cooled air.
Could it be something easy?
Bad valve under the dash?
Or am I looking at something electronic?
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1999 E320 (gave to daughter) 250K
1994 F150 (new engine installed!) 240K
1989 560 SL (Refreshing top end) 150K
1986 560 SL (deceased., gave it's life protecting my wife)
1988 300 TE (departed)
1994 945T (awaiting engine diagnosis) 349K
1986 242Ti (fallow)
1968 GT500KR (under restoration)
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  #2  
Old 04-26-2009, 04:45 PM
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It could be the duovalve, which is located right beside the component box under the hood. More likely the problem is that you are severely low on refrigerant.
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  #3  
Old 04-26-2009, 05:02 PM
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I can check the refrig easily enough. Thanks.
(Daughter currently has the car and is complaining, like her mom...)

If that isn't the problem how do I check the duovalve?
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1999 E320 (gave to daughter) 250K
1994 F150 (new engine installed!) 240K
1989 560 SL (Refreshing top end) 150K
1986 560 SL (deceased., gave it's life protecting my wife)
1988 300 TE (departed)
1994 945T (awaiting engine diagnosis) 349K
1986 242Ti (fallow)
1968 GT500KR (under restoration)
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  #4  
Old 04-26-2009, 05:45 PM
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One way to check the duovalve is to clamp off the pipe leading to the engine. Using an IR thermometer on the pipes going to the heater cores to check for a difference in temperature (controls both set to LO) would probably work fine too.
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  #5  
Old 04-26-2009, 05:50 PM
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It sounds like a broken rubber diagphram to me...

unfortunately, most of them are under the dash.
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  #6  
Old 04-26-2009, 06:30 PM
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OK, I'm leaning toward the busted diaphragm.
Air is definitely COLD coming from the pass side center & door vents and HOT coming from the driver side center & door vents.
Am I better off going in through the driver's side or the pass side to find the modulators?

By the way, is there a sight glass to check the R-134? Or can it only be checked w/a gauge?
__________________
1999 E320 (gave to daughter) 250K
1994 F150 (new engine installed!) 240K
1989 560 SL (Refreshing top end) 150K
1986 560 SL (deceased., gave it's life protecting my wife)
1988 300 TE (departed)
1994 945T (awaiting engine diagnosis) 349K
1986 242Ti (fallow)
1968 GT500KR (under restoration)
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  #7  
Old 04-26-2009, 07:28 PM
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No sight glass, and a set of gaugse isn't very accurate on a TXV system for this sort of thing, but if you know that the rest of the system is in proper order, you can charge by pressures (high and low, not just low).

Note that a restriction can cause warm left-side vents, as can a low charge, but with a restriction it will appear to have good pressure but still have very low flow.

Running a system with insufficient refrigerant flow will wear out the compressor due to insufficient oil migration.

There are not blend doors in this car, so looking behind the dash is looking the wrong place. However, you say hot air. Hot as in ambient, or hot as in heated? You're down south, so I really can't be sure; ambient is pretty darn hot for you, probably.

Turn the compressor off (EC button), put the controls on LO and measure the temperatures at the left-side and right-side of the center vent. If there's a difference, it's the heater and you have a bad duovalve. If there's no difference, you can completely quit suspecting that anything is wrong with the heater and it is only a cooling problem. Sorry, but I had forgotten this easy test before.
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  #8  
Old 04-26-2009, 07:48 PM
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It'll probably be low on refrigerant, not "severely" as stated earlier, but just a tad low. cooling off just the entry side of the evap, but not enough to cool the whole evaporator.
Gilly
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  #9  
Old 04-26-2009, 08:11 PM
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You're right; "severely" was a misstatement. However, because it is affecting system operation, you don't want to just assume that it still has proper oil migration.
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  #10  
Old 04-26-2009, 10:39 PM
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It worked fine last fall, hasn't been used (A/C) 'til recently when it showed up with this.
So I am leaning toward low refrig. or duovalve (anyone have a pic?).
Is the duovalve replaceable by me (coolant valve) or do I need to go to an A/C shop (refrig. valve)?
Will talk the kid through the checks tomorrow but I think it was heated air, not just ambient.
__________________
1999 E320 (gave to daughter) 250K
1994 F150 (new engine installed!) 240K
1989 560 SL (Refreshing top end) 150K
1986 560 SL (deceased., gave it's life protecting my wife)
1988 300 TE (departed)
1994 945T (awaiting engine diagnosis) 349K
1986 242Ti (fallow)
1968 GT500KR (under restoration)
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  #11  
Old 04-27-2009, 10:36 AM
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If it is the duovalve, you can easily change it yourself. That's just a water valve.
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  #12  
Old 04-27-2009, 06:14 PM
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OK, I had the kid do the test early enough this morning that is was still cool outside.
NO discernible difference in temp between the 2 center vents.
Ambient air temp. coming from both. No heat.

So this points to low charge?
__________________
1999 E320 (gave to daughter) 250K
1994 F150 (new engine installed!) 240K
1989 560 SL (Refreshing top end) 150K
1986 560 SL (deceased., gave it's life protecting my wife)
1988 300 TE (departed)
1994 945T (awaiting engine diagnosis) 349K
1986 242Ti (fallow)
1968 GT500KR (under restoration)
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  #13  
Old 04-27-2009, 09:16 PM
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Posts: 4,263
That points to low refrigerant flow, probably caused by low charge. My car actually had a restriction causing the same problem, but mine had a TSB on a defective dryer and I don't think it applies to the '99 MY. If you add refrigerant and get a good high-side pressure reading (at the gauge port, NOT using the climate control panel) but still have insufficient cooling, it's either a restriction or a bad TXV.
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