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Registered 2001 SLK320
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81 Posts
Discussion Starter #1
Haven't been around the site for a while...Been traveling... Also have not gotten to drive the SLK for over a month because of it. One of the first things I did was to take the car out for a exercise ride. It was a cold enough morning here in the mountains that I needed the heater. All was well, then I turned heater on. Gradually as the car warmed up the windows fogged up and the defroster would not clear them. I'm thinking heater core! This must be a horrific job to do! I can't think of anything else that would fog the windows but a heater core. The car is garaged and is not wet nor does it go out in rain. Just thought I'd mention that.
Has anyone had the honor of replacing a heater core?
 

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228 Posts
Haven't been around the site for a while...Been traveling... Also have not gotten to drive the SLK for over a month because of it. One of the first things I did was to take the car out for a exercise ride. It was a cold enough morning here in the mountains that I needed the heater. All was well, then I turned heater on. Gradually as the car warmed up the windows fogged up and the defroster would not clear them. I'm thinking heater core! This must be a horrific job to do! I can't think of anything else that would fog the windows but a heater core. The car is garaged and is not wet nor does it go out in rain. Just thought I'd mention that.
Has anyone had the honor of replacing a heater core?
Are you loosing coolant? Is the interior (passenger feet, driver feet) wet (damp) from coolant?

If not, excersise the heating and ventilation controls, check the ventilation fan, check under the intake plenum cover and check the "pollen filter" (AKA "cabin filter"). Is there a powerful air stream that can be directed as per controls? Is the internal/external air supply switch in "external" ?
 

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Registered 2001 SLK320
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81 Posts
Discussion Starter #4
Don't know when the cabin filter was replaced... what would that have to do with fogged windows? No signs of any leaks, no sweet smell or stains. HOT heat with good air volume, controls work fine. A/C has not been operated in several months. A plugged evaporator tray drain would have showed up during the summer and by now be bone dry if it were plugged. It's about a 1500.00 job at the dealer. We don't drive it much in the cold so after a real diagnosis I may by pass the heater core if that's what the problem is. I was hoping someone had done the Job...I've read for other models it's a 4-5 day job for a novice with no guarantee everything will work correctly afterwards. IF it's a heater core it sounds like my tax return is already spent
 

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Premium Member 2014 SLK200
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2,363 Posts
Cabin filters become surprisingly clogged after a relatively short service life and, consequently air flow becomes restricted.

The SLK cabin is of relatively low volume so condensation can form quickly.

That being said, if aircon servo motors give out or flaps jam, then direction of warm/hot air becomes compromised.

Anyone know if the SLK has an aircon 'self diagnosis' that can be initiated?

My Toyota RAV4 does - it cycles through all the various settings and will throw a code via the aircon setting screen.
 

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559 Posts
Haven't been around the site for a while...Been traveling... Also have not gotten to drive the SLK for over a month because of it. One of the first things I did was to take the car out for a exercise ride. It was a cold enough morning here in the mountains that I needed the heater. All was well, then I turned heater on. Gradually as the car warmed up the windows fogged up and the defroster would not clear them. I'm thinking heater core! This must be a horrific job to do! I can't think of anything else that would fog the windows but a heater core. The car is garaged and is not wet nor does it go out in rain. Just thought I'd mention that.
Has anyone had the honor of replacing a heater core?
See post 6 for a likely solution.
 

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Registered 2001 SLK320
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81 Posts
Discussion Starter #8
Cabin filters become surprisingly clogged after a relatively short service life and, consequently air flow becomes restricted.The SLK cabin is of relatively low volume so condensation can form quickly.
That being said, if aircon servo motors give out or flaps jam, then direction of warm/hot air becomes compromised.
Anyone know if the SLK has an aircon 'self diagnosis' that can be initiated?

I'm not sure that air flow is the cause but I'm going to check it out this AM! You never know how a gremline works till you look.
 

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Registered 2001 SLK320
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81 Posts
Discussion Starter #9
I had the same problem. Drove me batty till I figured it out. Took about 30 mins to fix. https://www.youtube.com/watch?v=KbQhC5OjvL4&t=87s
Thanks for the video! I'll look into the flap being open. We do use the A/C & heat with the top down depending on the outside temp. If it's the same problem as your car I'm still looking at a major repair unless I make something to pull it shut and open.
 

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559 Posts
Thanks for the video! I'll look into the flap being open. We do use the A/C & heat with the top down depending on the outside temp. If it's the same problem as your car I'm still looking at a major repair unless I make something to pull it shut and open.
Not really, I'll try to explain it a bit more. The flap allows you to recirculate air in the cabin. This gives you maximum AC output. When it sticks in recirc mode, as mine did, humid air get recirculated in heating operation leaded to fogging of all windows. By leaving the flap on outside air, you eliminate fogginess during heating but technically diminish max ac operation. This past summer, we hit 98f a few times and my car was very cold despite not having functioning recirc.

I went through the same process you did. Cleared the drain tubes, checked for damp carpets, checked for low coolant and everything was fine.
 

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Registered 2003 SLK200
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129 Posts
I had the same problem. Drove me batty till I figured it out. Took about 30 mins to fix.
Thanks for that. Misty windows and flap wide open on either setting.
Going to fix it now:Beer:

Update: That sorted it.
Now, I like things to work. Is it possible to replace the actuator?
I can find a drawing but no part numbers on the EPC. Anyone know?
 

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Premium Member 1999 SLK 5.4 M113
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1,440 Posts
wow, I cant believe I'm just now coming across this!

4.5 years I've had the car, and every winter it would fog up and freeze on the glass INSIDE the cabin... will definitely have to give this a shot!
 

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Registered 2001 SLK320
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81 Posts
Discussion Starter #14
Are you loosing coolant? Is the interior (passenger feet, driver feet) wet (damp) from coolant?

If not, excersise the heating and ventilation controls, check the ventilation fan, check under the intake plenum cover and check the "pollen filter" (AKA "cabin filter"). Is there a powerful air stream that can be directed as per controls? Is the internal/external air supply switch in "external" ?
I still have not had the time to pull the glove box out to check on that flap. I did have my wife exercise the controls several times the last time she drove it. That seemed to make things work. No fogged windows!! So relieved it's not a heater core!
THANKS!!!!!!
 

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228 Posts
I still have not had the time to pull the glove box out to check on that flap. I did have my wife exercise the controls several times the last time she drove it. That seemed to make things work. No fogged windows!! So relieved it's not a heater core!
THANKS!!!!!!
I can relate to that effect.

Good for you!
 

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Registered 2003 SLK200
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129 Posts
Today I went in search of the air flap return spring. I found it :rb

Its not as big as I thought, said the actress to the bishop....
35mm by 5.5mm. Now searching for something similar.
 

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