W210 CCU-- low refrigerant or duovalve? - PeachParts Mercedes-Benz Forum

Jeremy5848 · #1 05-22-2009, 01:44 AM

Today the wife complained that the '96 E300D (W210, OM606NA, 260000 4-owner miles) wasn't cooling like she thought it should. I did some checking. With the car idling in the driveway, I turned down both sides of the CCU to "LO" and put a thermometer in the center vents. The right side got down to 40F while the left side got no colder than 57F. It has been posted here that this is often a case of low refrigerant, less often a failed duovalve.

Next, with the CCU set to 72F both sides, the sensor values that I got (in Centigrade) were:
1. Inside temp = 22
2. Outside temp = 25
3. Left heater core temp = 15
4. Right heater core temp = 7
5. Evaporator temp = 19
6. Engine coolant temp = 90
7. Refrigerant pressure = 6
8. Refrigerant temp = 29

Next, with the car idling in the driveway and both sides of the CCU set to 72F, I put the CCU in "EC" mode and got cool-to-lukewarm air from both center vents (the outside temps were down to about 65F at this point). Then I unplugged the electrical connector at the duovalve and got hot air from the left side and cool-to-lukewarm air from the right side. Plugging the monovalve back in got rid of the hot air.

Checking the diagnostic codes, I got a bunch that probably were left over (I recorded them anyway). I cleared all the codes and ran the car again; the only code that returned was b1462, which is the wide-open throttle signal. Don't know what that could mean.

Finally, I exercised all of the flaps and got some strange results:
DTC 0 should close all flaps but I still get air from the left and right vents.
DTC 1 should open and close the left center vent; mine opens and closes both center vents.
DTC 2 should open and close the right center vent; mine won't open either one.
This seems to suggest a problem with one or more vacuum solenoids.

Tomorrow I plan to have my mechanic check for low refrigerant. I may pull the duovalve apart, following one of the threads posted elsewhere. The flap problems I'll ignore if at all possible--I'm sure pulling the dash apart would not be fun.

If anyone can see a pattern here, I'd like to hear from you.

Jeremy

Matt L · #2 05-22-2009, 10:05 AM

It sounds like you're not getting proper flow through the right side of the duovalve. That will cause a heat problem next winter. But maybe she won't notice, if she's in the left seat.

It sounds like they're both shutting off the flow, but your refrigerant level is low causing the warm left-side vent.

I don't know about the flaps, sorry. The WOT error comes and goes for me too. No troubles as a result.

Jeremy5848 · #3 05-22-2009, 11:31 PM

Found a good test to answer my question in another forum:

1. Set both sides of PBU to "LO" (duovalve should be fully closed), push "EC" button (light is on) to turn off a/c compressor, measure temp on both sides of center vents. Result: both sides blow air that is about the temperature of the outside air, maybe a bit warmer because of engine heat in the driveway.

2. Now press "EC" again (light goes off) to turn on a/c compressor, measure temp on both sides of center vents. Result: right side much colder than left side.

Conclusion: duovalve OK, a/c system low on refrigerant. Will visit mechanic on Tuesday to have system checked and freon added as necessary.

Jeremy

Matt L · #4 05-23-2009, 09:42 AM

Sounds like the problem. Don't overfill it.

Jeremy5848 · #5 05-26-2009, 03:20 PM

My indy ran some checks and found the a/c system low on refrigerant. He added 1 pound of R134A and both driver and passenger zones now get down to 39-40F.

For those who are thinking of getting a license to DIY, this pound of refrigerant cost me a total of $130.44 including labor (northern California prices, including our new 9.25% sales tax). Depending on your particular circumstances, the cost of the license, equipment, and supplies could easily be justified.

Thanks for your help with the diagnosis.

Jeremy

KarTek · #6 05-26-2009, 03:22 PM

R134 is licensed in CA???!!!

I'm studying for my type 608/609 so I can buy R12 and service home HVAC but I didn't think it was required to just buy and charge small quantities.

Jeremy5848 · #7 05-26-2009, 07:10 PM

Quote:

Originally Posted by KarTek

R134 is licensed in CA???!!!

I'm studying for my type 608/609 so I can buy R12 and service home HVAC but I didn't think it was required to just buy and charge small quantities.

The service sheet says "R134A - 16 - ounces - $3.00/ounce - $48.00." I didn't look at the pressure container to see what it really contained. What California law requires I do not know, maybe someone else can advise us.

Jeremy

TMAllison · #8 05-26-2009, 07:32 PM

You can buy R134a over the counter. I believe R12 requires a license.

Matt L · #9 05-26-2009, 09:11 PM

You need the 609 license and you are required to have certified equipment if you are doing jobs with R134a for hire.

For personal work, or non-hire work for friends, you can use non-certified equipment as long as it meets certain performance parameters and you do not need a license (except in Wisconsin).

I paid $90 for a can of 134a, which comes out to about .19/ounce.