E320 a/c problem - PeachParts Mercedes-Benz Forum

rjk · #1 04-26-2009, 04:44 PM

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?

Matt L · #2 04-26-2009, 04:45 PM

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.

rjk · #3 04-26-2009, 05:02 PM

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?

Matt L · #4 04-26-2009, 05:45 PM

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.

J.HIDALGO · #5 04-26-2009, 05:50 PM

unfortunately, most of them are under the dash.

rjk · #6 04-26-2009, 06:30 PM

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?

Matt L · #7 04-26-2009, 07:28 PM

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.

Gilly · #8 04-26-2009, 07:48 PM

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

Matt L · #9 04-26-2009, 08:11 PM

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.

rjk · #10 04-26-2009, 10:39 PM

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.

Matt L · #11 04-27-2009, 10:36 AM

If it is the duovalve, you can easily change it yourself. That's just a water valve.

rjk · #12 04-27-2009, 06:14 PM

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?

Matt L · #13 04-27-2009, 09:16 PM

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.