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Old 05-26-2006, 01:21 PM
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Join Date: Jul 2001
Posts: 71
201 Heater Valve

My 1989 190e, with the A/C on is blowing hot air out of the side vents only on heavy or uphill accelerations. Once the car reaches coasting speed the air goes cold again. Center vents continue to blow cold all the time. I replaced the vacuum regulated heater control valve but still have the same problem. I've looked at the vacuum lines and they look good. Is there a vacuum check valve that goes bad in this car? If so, where is it? Thanks!

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Old 05-26-2006, 02:27 PM
irieite's Avatar
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Join Date: Nov 2002
Posts: 157
Most likely, one or more of the vacuum actuators are leaking under the dash. This is common. There is a vacuum switchover valve located just to the right of the glove box. Remove the glove box and test each line, one by one with a Mighty Vac and you will find the leak. The interim solution for me was to cap off the leaking actuators, in order to stop the heat.
2000 c280 Sport (looks like an upgrade, feels like a downgrade)
1991 190e 2.3 (sold)
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Old 05-26-2006, 03:56 PM
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Join Date: Jul 2004
Location: York, PA
Posts: 621
A vacuum leak anywhere in the system will cause that. And yes there is a check valve as well. Even the slightest vacuum leak in the engine bay can cause this problem. What is happening is that when accelerating the vacuum drops to low for the HVAC system to keep the proper pods open and closed. There is a check valve and a vacuum resevoir on the HVAC side of it to keep vacuum steady during acceleration. But if a pod leaks or there is a cracked rubber connector on a vacuum line they you will have a loss of vacuum causing the HVAC to default to its no vacuum state which is full heat, opens the blend air doors, and also full defrost since that defaults to open as well. So you could have a bad pod, bad rubber connector in the vacuum lines, bad check valve, bad resevoir or line to it, or a leak in the engine bay.
2003 Pewter C230K SC C1, C4, C5, C7, heated seats, CD Changer, and 6 Speed. ContiExtremes on the C7's.

1986 190E 2.3 Black, Auto, Mods to come soon.....
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Old 05-26-2006, 04:01 PM
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Join Date: Jun 2000
Location: Saugus, CA USA
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Mine did that. I couldn't figure out for the life of me how the climate control could tell that I was going up a hill
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Old 05-30-2006, 11:09 AM
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Join Date: Jul 2001
Posts: 71
Thanks for the advice! I spent some time looking at the vacuum hoses and rubber connectors and could not find any obvious leaks under the hood or in the dash. Where are the check valve and vacuum reserve located?
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Old 05-30-2006, 11:43 AM
GVB GVB is offline
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Join Date: May 2006
Posts: 178
Your heater valve is whats leaking. It is the red vacuum hose, it goes just inside the dash on the passenger side. You will have to remove the right side plastic screen for the venalation inlet. The valve is spring loaded, and reverts to full hot when goes bad. You can test it using a vacuum gauge, it gets its source from the drivers side, it is the white vacuum line going into the cabin, and it splits right at the firewall, pull the red vacumm line off and see if it hold vacuum.

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