'92 300SE.
Took the car on its first long road trip last weekend. About 1,000 miles between Thursday AM and Sunday PM.

Car ran flawlessly, with the exception of the A/C. I recently had it evacuated and recharged at my local MB indie, the system was slightly low on freon.

I'm having trouble with the system freezing up. On the outbound journey, at about 2 hours into the trip, there was virtually no airflow from the vents. Setting the fan to high speed only resulted in lots of blower noise. Choosing Auto, floor, middle, upper, defrost made no difference, although we could hear the vent dampers cycling as the settings were changed.

Cut the system off for a while and when restarted, nice airflow and cold air. When we arrived at our destination and stopped for about 2 hours, there was a HUGE puddle of condensate water under the car - far more than I would have ever expected. I think this confirms the freeze-up situation.

I'm planning on taking the car back to the indie for more work to get this sorted out. I'd like to be armed with as much info as I can get.

Prior experience with A/C units that freeze up have always pointed to low freon level. I'm going to assume that's not the case with this unit since I'd had it filled less than 2 weeks ago.

NO - I don't know whether the evap has been changed. Obviously, the first check will be to see if the system is low again, and if low, a leak test to see where the loss is. I'm not initially inclined to believe its the evaporator - the car sat for almost 2 years and the A/C was only slightly low at that point. I've put almost 10K on the car since July and the A/C has always blown cold, but at moderate outdoor temps was prone to freezeup, and I could see bubbles in the dryer sight glass, which is why I sent it in for service.

Any suggestions would be appreciated.

Very common on the early W140's..MB issued "memo" not bulletin on that problem back in 1995...suggests a replacement evaporator temp sensor & the addition of 1K ohm resistor to that sensor.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

can you provide details - i.e. is there an updated evap temp sensor part #?, and also where to install resistor?

Thanks!

Latest MB number is 210-830-07-72..stick with OE BEHR sensor.

A resistor can be soldered on either wire to the sensor. simply cut or de-solder wire & insert the resistor between the cut wires.

A 1/4W or 1/2W resistor will do.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

If the system has cabin filters check them. I have seen where dirty cabin filters will cause the system to ICE up.

__________________
Dennis
2006 E320 CDI Black/Black Leather. Nav, HTD Seats HK stereo 32000 miles.
2000 VW Passat 1.8t 300,000 miles as of Dec 09, 2009 original owner
1997 E300d Silver 300,000 miles As of Jan 05, 2010
3rd owner SOLD