Hi, Today I tried to use my A/C for the first time in approx. 1 month (worked great when I used it last) and it would not blow cold air, only what felt to be ambient temperature (not hot). I moved the temp. wheel to hot and hot air came out just fine. Does this mean I can check off the pushbutton control unit as being faulty? I have searched all the posts relating to 300E a/c but alot of the lingo is just a bit beyond my knowledge of where the components are under the hood. I know where the Klima unit is and the compressor, but thats it. I have replaced the fuses that are key to A/C (#7, #D). What is my next step in diagnosing the problem? Also, I have heard that the OVP has been the freak cause of my A/C problem in some instances... 2 weeks ago the car began having a hard time starting when cold (not cranking but firing) which I have read is also in some cases the OVP. Is there any way to test the OVP- could this be the solution to both problems? Thanks everybody! Jerry

__________________
05 E55
03 E500

You need to start by putting gauges on the a/c system and check the charge. Also look to see if the compressor clutch is engaging when the a/c is turned on max. If it is not, you will most likely find that the refrigerant charge is low.

If the charge is indeed low, it had to leak out. You need to locate the leak before recharging.

Good luck,

Thanks for the quick reply Larry!

Yesterday I had my friend check the charge with his guages (he is more familiar w/ A/C than I am). It registered as full. Also, there is a little green sticker under the hood that states my A/C system has been equipped with tracer dye. Does this mean that I will notice any possible leaks when I see the color of the dye around the A/C equip. (I don't see any dye)?

Where is the clutch in relation to the compressor and how do I check to see that it is engaging?

I getting more information about the OVP relay and I am finding that not only is it sometimes the freak cause of sudden A/C failure but also makes the cruise control malfunction which it has been for the past six months. I am going to open up the OVP rlay later today to see if I see any loose points in the elec. contacts.

Thanks!

Jerry

__________________
05 E55
03 E500

Yep, sounds like OVP problems. The first simple step for this situation would always be a quick check to see if you have a low charge.

The Tracer Dye is UV. If the charge ever leaks out, you will be able to use a black light to find the leak.

Good luck,

OK, I replaced the OVP with the single fuse KAE aftermarket replacement. Nothing changed.

I am only a beginner w/ all this auto-troubleshooting stuff but it seems like everything I research on MercedesShop points to the OVP (except lack of ABS light illumination). My cruise control surges, a/c suddenly dead, and hard starting when cold. Then again I guess this could be three seperate problems...

Any more suggestions out there? Did I get a bad OVP?

Thanks,
Jerry

__________________
05 E55
03 E500

It may not be the cause of your aircon failure but i had the same experience and here is what happened:
If the auxiliary fan does not start up at the proper engine operating temperature, the aircon solenoid switch can overheat and malfunction and the fuse pops. You can then lose your freon fairly quickly. Once i had the auxiliary fan fixed, it came on at the right temperature, no more problems. it required recharging the freon. If you have a hose leak(there are two), then you can have a leak as well. The garage initially wanted to replace most of the aircon, including the compressor but i explained that the compressor will not start up if there is no freon.

Heh. Thats how my 300E works anyway.Hopefully.

al