560SEL Defrost Blows Hot All The Time
 

On my 560sel - heater and A/C functions with Climate Control work normally. However - if I get a mist on the inside of my windshield and put the defrost on - the blower goes on high and real hot air blows onto the windshield. OK for winter - but in the summer - a lot of extra heat. Turning off defrost allows normal operation of CC. Is this normal operation or is there a function of the ccu that determines the defrost air temp depending on if the A/C is on or the heater is on? On all my other non-Mercedes cars - if you put the defrost on - the temp is the same as is coming out of the vents - whatever you have it set to.

moedip,

I believe that is normal. The A/C should be on also to dehumidify the air before it reaches the heater section. There the dehumidified air is heated, further dropping its relative humidity, and the hot, dry air is directed at the winshield and side windows to clear them up. Once the windows are clear, the defrost feature can be turned off and a "more appropriate for the weather conditions at hand" setting on the climate control can be selected.

I agree the selections on the system are not what I would prefer but they seem to do the job. Newer models have a sysem that is more readily customized for the user's needs, but they still limit the number of choices in ways that make me wonder.

Jim

I agree Jim - seems strange that on an expensive car (when new) you have limited option but on an inexpensive car you have infinite selection. But I have to admit - when you put the defrost on - it really clears the window fast! Thanks for the info

Mine runs high if the blower switch is in the auto position, but will go to low if I select that blower button. I believe the hot and cold detent positions run the blower high in the auto mode, and you can manually select low speed.

Greenacres2 - but does it blow full hot air on auto and low speeds when defrost is on???? If it does - I prefer a fast sweat than a slow melt on low from the heat delivered.

I may have misunderstood
 

I thought you meant it blew high speed if you set the temp dial to the defrost detent, and were looking for a way to reduce blower speed. If you want a lower temp air blowing to the windshield, that should happen by pressing the directional control without changing the temp. I usually use the windshield/feet button, and as I sit here I can't recall ever using the windshield only (it was a very mild winter).

If I understand my manual correctly, the temp wheel governs temp plus switches blower to high speed when set to the full cold or full hot position if the blower is set to auto. Directional buttons determine outlets where airflow is directed. As for fan buttons, top is always high, auto is auto unless temp is at high or low detent, and low is always low.

It's about 90F here today, so I'll run through all my settings on the way home and see if the windshield only directional button changes temp in my car.

Now you got it!! I'll await your response. Just push the full defrost button in and see if the temp goes to full hot- then returns to what your dial-a-temp knob is set to when you take it off defrost. If it doesn't go to full temp. in defrost then I have another glitch to work on.
thanks

Well I'll be...
 

It does go to full hot when you press the defrost button. When I pressed the bi-level next to it though it went back to the dial setting but kept some air on the windshield. That will be handy to remember in colder weather for a quick defrost. The warmer weather solution might be to use use the bi-level and dial the temp up a touch--slow roast:D .

Tried mine today after reading through this post earlier. Sitting at school waiting to pick-up the kids ACC set to a comfortable 70dF or so on "auto", fan running at low speed.

I hit the defrost switch, air moved to the windshield and turned HOT. Soon as I switched back to bilevel, the air was coming out as cool as before.

That makes three, sounds like normal.

I'd guess that for normal inside window fog, bilevel would be fine, but for the first warm of the windshield in the morning, or dead of winter driving, then use the defrost button.

Thanks mike and greenacres2 - It just seemed odd - not a real problem. Now i know it's normal.Sounds like a quick way to heat interior without moving the dial-a-temp for starting up in winter.
Thanks for verifying
maurice