W124 A/C after a few hours driving - Page 2 - PeachParts Mercedes-Benz Forum

#16 06-17-2004, 08:29 AM

My Ohio 89 300se has just started doing the same thing. I use the car for cruising around town (a/c fine) and road trips (a/c dies suddenly after 1/2 hr). Mechanic says freon level is fine and system is cycling. Should I be looking for the same thing?

Q-Ball · #17 06-17-2004, 08:43 AM

I would say yes. Once I get part installed, i will report my findings.

FQ

#18 06-17-2004, 09:10 AM

Oh yeah. The mechanic says he needs to see car when a/c is not working but he'se thinking bad expansion valve ($700, gulp).

#19 06-17-2004, 09:15 AM

Oh yeah. The mechanic says he needs to see car when a/c is not working but he'se thinking bad expansion valve ($700, gulp).

kidMoBile · #20 06-17-2004, 09:52 AM

First let me state for the record that I don't know jack about AC. That being said, I had the described condition in my house AC, where it started out cold but gradually over several hours lost both airflow rate and cooling ability.
My evaporator was icing up as it turns out. The HVAC technician who came out to fix the problem said that it was a simple matter of the system having a low freon charge. He added 1 lb of freon to the system and the problem was solved.
His explanation: The low charge of the system was allowing the freon to evaporate too quickly at the evaporator, so it actually was too cold at the evaporator leading to the icing condition. Over time the ice chunk just blocked flow of air through the ducts. If the system were at proper pressure, freon evaporation would be a bit slower and thus not as much of a temp drop (not enough to freeze water, only condense it). This made perfect sense to me.
I only bring this up because it may be a simple fix. Again, I don't know jack about AC and a car's system will certainly be different from my house.
Brian

Q-Ball · #21 06-20-2004, 12:16 PM

I ordered and received part from fastlane, 25 bucks or so. Took apart lower panel below sterring wheel, about 30 minutes. Located evaporator sensor and replaced it, very simple, and all seems ok as of now.

I have yet to drive for more than an 50 minutes or so on the highway, but my temp. readings were consistent as the a/c cycles. This week i should be on a 2 hour drive, and if any symptoms are to come back, it should happen then. I have my fingers crossed, because i hope this will fix the icing up problem.

FQ

Q-Ball · #22 07-11-2004, 10:34 AM

Part is installed and was no to difficult to put in.

Made 2 trips this weekend of over 2 hours in duration. On one occasion at about the 2.5 hour mark, i noticed a/c dimidnishing in cooling capacity. i stopped for fuel, and popped the hood, sure enough ice was all over leading to the evaporator. It only took 10 minutes or so in the 91 degree heat in the sun to melt. A/C worked fine after that. On my return the a/c blew cold the entire way for 3 hours, again in 90 degree eat. I am not sure what is causing this, but i will continue to live with it. I am not convinced that the temp switch made any differenc...yet.

stevebfl · #23 07-11-2004, 11:13 AM

Does the cycling that you have observed during proper operation change before the event?

Does the compressor stay engaged? unfortunately the pressure of the low side would be a better way to watch the event.

If the evap is freezing the cycling temp should drop before the temp gets warmer. All of this can be distorted if not watched in "Min" position. In other positions temp is modified by hot air mixing and the temp is no longer evap temp. I have seen evap temp sensors covered internally and give too high of values and thus the temp gets too cold before cycling.

brewtoo · #24 07-11-2004, 12:12 PM

I used to have an '86 300E that would do the same thing on trips. When I would notice the air output starting to warm, I would simply press the EC switch and let the ice melt. The air output would stay quite cool for a good while because of the ice. When the ice melted, I would turn the AC back on. Seems like I had to do it every 40 minutes or so. It would take about ten minutes to melt while driving.

One way to tell if it's freezing at the evaporator...park the car when you think it's frozen. If tons of water leaks out under the car, you know it was ice melting. That's what mine did.

Never did fix it, btw. Just learned to work around it.

MB_FanAddict · #25 07-11-2004, 01:36 PM

Q-Ball,

What did you have the ACC set to during the trip?

Chris

Q-Ball · #26 07-11-2004, 03:42 PM

I will check cycle temperatures again tomorrow.

I did also think about turning a/c to ec, to help melt ice. I keep the A/C set to around 75, and always on auto and let it do its thing.

I am driving 3 hours on friday, so we shall see how it goes.

Thanks guys.

Q