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  #1  
Old 03-07-2007, 08:27 AM
fireman1073's Avatar
fireman1073
 
Join Date: Nov 2005
Location: new bedford Massachusetts
Posts: 152
help! haunted heat

My climate control on my 84 300sd is haunted.

Only first thing in the morning the defroster will work but if i put it on any other setting the fan stops and cold air comes out the center vents.

After a while pushing buttons it will work normal for the rest of the day then the next morning same thing occurs.

changed the engine temp interlock

I have grounded the engine temp interlock.

tried different temperature regulators.

fan speed controllers 2 different ones

ccu 5 different ones

soldered ccu

changed interior temp sensor 3 times

unplugged electric water pump

And yet the same thing occurs

occasionally it works right.

I can't figure it out

any ideas?

Steve
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  #2  
Old 03-07-2007, 09:18 AM
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Join Date: Oct 2006
Location: Pennsylvania
Posts: 333
Normal?

I'm not familiar with the 126 but what you're describing sounds like normal operation to me. On my 123 the blower won't operate on anything but defrost until the engine warms up to a certain temp. (Can't recall the exact temp tho)
I would assume the 126 system is set up the same way.
FWIW- My Chrysler Concorde has climate control and behaves much the same way.
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  #3  
Old 03-07-2007, 10:10 AM
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mmmmmm Diesel...
 
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Location: Royse City Tx
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Defrost is a system override like using high or low fan settings instead of automatic.

Mine does the same thing. I'm glad it does that so that I do not get an icy blast. BTW, I have to do vacuum work on the HVAC system. Air is split between all the dash vents and the windshield vents.
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  #4  
Old 03-07-2007, 10:14 AM
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Location: Evansville, Indiana
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Replace your monovalve insert, it's likely wrinkled or torn, and isn't feeding much water through the heater core. On Defrost, you get high fan and full heat (Monovalve constantly energized), so the blower will run at 3/4 speed or something.

You will have very low speed fan and cold air (higher fan speed but still cold air on high fan) until the heater core warms up.

Verify that the aux pump works, too, and that you are full on coolant. Also, if the thermostat is bad, it will take forever to heat up (you should run just above 80 C rather quickly).

Peter
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  #5  
Old 03-07-2007, 10:16 AM
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Location: West of Ft. Worth. TX
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Pretty close to normal.........the fan should not come on, in other than defrost, until the temp sensor on the thermostat housing senses warm coolant.
However, it does sound like you may have a fresh/recirc vacuum pod leaking. It's located behind the glove box, about $50 for a replacement.
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84 300SD 350K+ miles ( Blue Belle )
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  #6  
Old 03-09-2007, 08:30 AM
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Quote:
Originally Posted by SD Blue View Post
Pretty close to normal.........the fan should not come on, in other than defrost, until the temp sensor on the thermostat housing senses warm coolant.
However, it does sound like you may have a fresh/recirc vacuum pod leaking. It's located behind the glove box, about $50 for a replacement.
I bypassed the temperature interlock on the thermostat housing to eliminate that but i agree on the vaccum pod leak idea.

I can leave the heat on all day and it will not turn on unless i hit defrost for a while then switch back to EC heat button then it might work.

I must have bad climate control units, I will solder another one and try that.

Mono valve is good also and so is the thermostat.

Once it starts working it will work normal for the day.

Is there another temperature sensor for heat other than the one on the T housing?

Steve
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  #7  
Old 03-09-2007, 11:24 AM
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From looking at the schematic, your temp. controller (mounted above the passenger footwell) may be temperamental. Or it may be an input to it such as the heater air temp. sensor or the in-car temp sensor. There is a connection between the temp. controller and the pushbutton control labelled "heating enable control" that controls power to the aux. pump. and, through circuitry, controls the mono-valve.
The pushbutton controller, for the most part, switches the modes but a lot of that is controlling the vacuum pods for air direction. But since it is mechanical relays and switches, it is prone to the most failures such as cracked solder joints.
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