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