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Old 01-15-2001, 01:09 PM
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heat valve installed but still no heat....i tried posting about this problem previously but got no response. have changed the mono heat valve in my 88 sel but still have no heat. when put on defrost will blow hot air towards windshield but cold out side vents...freezing in ks last couple of weeks. am i missing something?

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Old 01-15-2001, 01:47 PM
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Join Date: Jul 2000
Location: Sunny Florida
Posts: 199
Is your car getting warm enough to produce heat? Could be your thermostat is stuck open.
What temperature does the dash indicate?
1989 560SEL (172k)
1989 325IC (122K)
2004 Suzuki Volusia LE (3500 miles)
2005 Yamaha Road Star (20 K miles)
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Old 01-15-2001, 11:50 PM
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the thermostat has been replaced already and the temperature gauge indicates that the car is operating in normal temp ranges...marley
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Old 01-16-2001, 05:50 PM
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Join Date: Jan 2001
Location: the Netherlands
Posts: 1,417
When the heater does blow hot air (towards the windshield) but not through any of the other ducts, I think one of your valves inside the heater housing is not controlled any more (due to a vacuum leak or broken vacuum pod).
A valve has to be opened inside the heater housing to let the incoming air flow through the heat exchanger so it gets warmed up.
My guess is that this valve stays closed and the incoming air is being led straight into the interior...

1990 300SL-24
1993 C250D
with a minor 600+k kilometer
(the Netherlands)
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Old 01-16-2001, 06:49 PM
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this would be a different vacuum system than the one that controls the doorlocks ect....all of the vacuum controlled equipment appears to be working fine. how do i go about rectifying this problem or is it something that i can't do by myself???? thanks for the marley
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Old 01-16-2001, 08:45 PM
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Join Date: Nov 1999
Location: Germany
Posts: 63
The two vacuum systems you mentioned are separate and not related. Replacing the heater solenoid valve/mono valve is not enough to correct your problem. The a/c switch assembly is the first place to start your investigation, as it controls all the opening and closing of the air flow vents.


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