2000 C280 AC control unit issue
 

2 headed issue. 1st my fans speeds on my climate control system speed up and slow down too sporadically. More like it runs very slow on auto (with a slight whistle) until I push the fan button for manual up to high speed. Then it does go on high just fine.

Along with the fans...Over the past year+ my AC has been getting weaker and weaker. I speculated that hot air must be getting into the system as when the car starts on a hot day or after it has had a chance to warm up and i restart it, the AC will blow hot air at first through the AC until the compressor get AC going. But even then you can sense heat getting into the mix. So finally at the end of the heat last year it quit being cold all together. To the opint that if you run the AC at any temp setting you can feel a low amount of hot air coming from the vents?

I am about to get the freon recharged since the temps are getting to the 80-90 temps again and I suspect it to be my climate control module but is there something else I can check in the dash such as wether the vents by the heater core are cracked or not closing allowing hot air into the mix?

I just dont want to get it charged and then have a hot air mix on 100 degree days here in texas all summer.[/align]

RE: 2000 C280 AC control unit issue
 

Hi there, I'm quite fluid in all things A/C.... I would just like to provide some guideance here. A/C systems are closed loop. Basicly what this means is no R134a sholud be leaving your system, and no air/water/anything should be getting in the system. The properties of R134a are such that provided there is no major leakage you should get many years of trouble free performance.

Now here's the rub; most of your tubing joints around the compressor / evaporator / and other components still have BUNA-N rubber (I believe) o-ring that degrade over time. At diffrent points in the system you have diffrent pressures and the o-rings may have a small leak somewhere causing your overallR134a inventory to drop. This ultimatly means your not getting the most efficent thermal cycle from your system.

Once you recharge, the pressures change during and afterthe maintainence process (drain and vent) and the degraded CAN O-ring will leak more and sometimes everythings fine. You may find you A/C will be back to it's old self in several days or weeks if you've got a big leak.

O.K. Summary: get your mechanic to check the system for leaks before the recharge and avoid having it done again later. Typical A/C recharge service is 80 bucks at the budget places, and I never asked the dealer what it would take...The leak check should only involve use of a UV light. I think most systems have UV leakcheckput in from the factory now in the PAG oil charge. I don't know about MB though. Just check with your mechanic. If you get a leak and have to go back it's just more inconvienent for your and possibly more money at the repair that you could have found earlier.

Just my 2 cents!

Good Luck!

RE: 2000 C280 AC control unit issue
 

Oh, sorry,I forgot to mention... Fixing your A/C may fix the fan issue, like if your climate control is trying to make the temp 70 degrees but the A/C is'nt doing its' job the fan will go faster, and vice versa with heat and defrost....

I'm not sure about that though, but fix the A/C first and then see what happens.

Thank you for the tips Engineerd. My solution last year was to park it over the hot months and drive my 4 cyl pickup to and from work. Then in the fall take her back on out when it wasn't so hot.

OK I did take it to two different places for a check. The first place a quick shop did AC testing for $25 and they said that the system wont let them add anything to it? As in the vaccuum was sealed and they couldnt do anything. Which may be inline with what you said. I next took it to an AC specialist and of course their response was everything under the sun needed to be replaced.

I was reading that the sensors behind the AC module may be locking the system allowing false negatives to occur. Have you heard anything like that before? I was going to 1st try replacing the climate control module as I cracked the LCD one day during an attitude readjustment.