The other night we had a real nasty thunderstorm here in New England and I found to my surprise that my defroster only works with the temp wheel all the way on max heat. How lovely it was to be traveling with that terrible wiper, and having the heat full blast in 95 degree weather.

Any ideas on what to look for here? My AC does not blow out cold air to begin with, but I suspect it just needs a recharge.

Thanx

------------------
1987 300E

[This message has been edited by Webmaster (edited 07-05-2000).]

You would need the A/C to be operational for your defroster to work, since the A/C decreases the humidity in the passenger cabin which causes your windows to fog up. You would need to jack up the temperature to achieve the same effect without A/C operating. So I think you should get your A/C fixed.

In terms of your windshield wiper, you must have the single arm wiper common to all W124's. I've always found the wiper to be very good, even in the worst of weathers. Maybe the plastic blade needs to be replaced. If after replacing the blade you still find the wiper insufficient, you might wanna invest in a bottle of Rain-X, which is a pleasure to drive with especially on the highway or any other stretch of road where you can drive 60kph+.

------------------
-= 1995 Mercedes-Benz E420 (W124 - Black Pearl/Black) =-

Spinedoc, all of the 300E's go to full afterburner when defrost is selected on the climate control panel. Ther is no way I have found to adjust the temp or fan setting, unless both of my 300's are screwed up. If the A/C is not working you will still get max heat but it will be a little more humid than it would be with the A/C on line. Nature of the beast.

------------------
Jeff Lawrence
1987 300e
1989 300e
1987 BMW 325

[This message has been edited by Webmaster (edited 07-05-2000).]

[This message has been edited by stevebfl (edited 07-06-2000).]

Duck I guess I should have my AC checked out then, and in regards to the wiper, I have a new blade and use Rain-X religiously, I still think the wiper stinks.

Do a search and tell me that A/C complaints dont comprise a good 20% or more of posts on this site. Plus what do you mean only one temp position for defrost? The temp wheel and the defrost button are separate. I have owned a lot of cars and have never had one which would not blow cold OR hot air in defroster vents depending if ac was on or off.

Thanx

------------------
1987 300E

[This message has been edited by Webmaster (edited 07-05-2000).]

It is truly a PAIN driving in a storm when the wipers aren't working properly (it rains A LOT up here in Vancouver so I can relate). Ruling out bad wiper blades, could it possibly be something wrong with the "mechanics" of the wiper??? You might wanna check out the motor controlling the wiper assembly. I've noticed that it is quite powerful, when it makes a sweep and goes back to the resting position, I can feel my car wobble a bit. If the motor isn't "up to par", that may be the problem. Also, the wiper should be sitting on your windshield with the correct amount of pressure...maybe the adjustment got messed up. Anyhow, since you are goin' to get your A/C looked at, you could always go tell the mechanic while you are there that the wiper isn't workin' properly...and maybe he can take a look at it. Good luck!

------------------
-= 1995 Mercedes-Benz E420 (W124 - Black Pearl/Black) =-

And to clarify, in case my original post was not clear enough, with defrost on full, if the temp wheel is set to full heat then it blows hot air, otherwise nothing blows out. All the cars I have owned if the a/c is on, or the temp set to cool blow cold air out of the defrost vent, what part of that do you not understand. And by the way, in summer cold air "defrosts" just fine without raising the temp in the car.

------------------
1987 300E

[This message has been edited by Webmaster (edited 07-05-2000).]

Duck you mention that if my AC is not working correctly I would have to crank the temp wheel all the way up to get defrost. This is exactly what is happening.

Any ideas where I should start looking? Anyone else have any ideas or know if this is a known issue with the A/C?

Thanx

------------------
1987 300E

The W124 ACC's temperature selection thumbwheel is bypassed in the "Defrost" mode. When using the defroster, forget it exists; if functioning properly, the system recognizes no input from the thumbwheel nor the fan speed buttons in "Defrost" mode, as it is hardwired to simultaneously activate the A/C compressor, the heating system, blower motor and vacuum flap elements at certain settings. No user imput is recognized. If the defroster works only with the thumbwheel in "Max" heat position, you have a concurrent second problem, in addition to the A/C, probably the ACC pushbutton control unit.

In the defrost mode, power is sent to the A/C compressor clutch, so as to bring the compressor on-line, and the blower motor is sent to maximum speed; at this point the A/C system's primary job is not to cool the vehicle's interior nor maintain a pre-selected interior temperature but to provide cold air in the vicinity of the windshield so as to assist in dehumidification.

Where to start? Visually check the compressor's clutch when "Defrost" is selected; you should hear a subtle click and see the clutch start turning. If the clutch is not operating you either have a low freon situation or an electrical problem. If the clutch is functioning and the compressor operating, inspect the receiver/drier's sight glass; a continuous stream of bubbles is indicative of a low freon charge. The balance of the diagnostics rapidly diverges after this, depending on these initial findings.

M-B's W124 ACC service manual details pushbutton control unit and temperature thumbwheel diagnostics; rebuilt pushbutton control units are available from companies such as CCI/Uptime for a fraction of the price of a new unit.

jgl1, thank you so much. Now I understand how it works. I have long suspected my ACC pushbutton unit of being on the fritz for other reasons than this.

I will go thru the diagnostics you mentioned. You also mentioned a company with less expensive pushbutton units, do you have a website or phone # for them?

Thanx again for the explanation.

------------------
1987 300E

There are several companies that offer refurbished M-B electronic components; check the M-B Club of America's publication [The Star] for a full listing of advertisers: one company is Beckman Technologies (800-742-1021); another, CCI/Uptime may (?) now be selling only through resellers such as the Brinson Co. (800.434.8788). You may also want to check this site's "Parts Shop" for availability. Expect to pay approx. $210 for a refurbished pushbutton control unit.

M-B's part no. for the Model 124 Automatic CLimate Control Service Manual is S-2380-000. For those interested, the manual offers a thorough explaination of individual components and nominal values but please note that ACC component testing and fault diagnosis in this model is not for the average DIYer.

Anyone know where a schematic of the climate control can be had.
1. I prefer to have my '95 E300D defrost fan speed submit to fan speed controls not default full blast.
2.The temp control in defrost needs to be subordinate to temp dial so my eye balls don't dry out and my brain doesn't become fried. I can only tolerate the defrost for a few seconds, it is rediculous.
3. Also would prefer to disconnect air compressor from this function since as soon as defrost is necessarily disengaged the condensation in the heat exchanger immediately fogs the windshield and I contiually have to switch back and forth from defrost.
The Mercedes climate control system is the absolute worst I've ever experienced and it is awful. It does not allow for individual manual settings. It is from late 70's-early 80's. I was aghast when I discovered mercedes carried this antequated system over from the earlier '84 300d model I owned.
Thank you!

__________________
'96 C220 138,000mi, '95 E300D 239,000 mi., '87 300TD 214,000mi '88 6.2 Turbo Diesel Chevy Conversion Van 253,000 mi.