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  #1  
Old 12-13-2005, 10:37 PM
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Join Date: Nov 2002
Location: Dallas
Posts: 802
Climate Control mystery is maddening-help please

I've been slowly chasing a climate control problem in my 1984 300SD for about 6 months...

'84 300SD W126 - A/C clicks off dead once it reaches dialed in temp

When the A/C kicks in - it cools very well. I thought I had an issue with the push-button climate control unit as it would cool the car down to about the point where you had the temperature dialed on the temp wheel and then the whole system would go "click" and go dead. Dead as in no control of the climate control using the push buttons or the fan speed (no response). Then after 15 seconds or so the unit would "click" and slowly come back to life and start cooling the cabin down.

In an unrelated event, at some point this summer the A/C stopped being directed towards the center vent and now goes through the dash defrost vents (ugh).

My Climate Control was actually a Programa rebuilt unit out of Boca Raton FL. Luckily I had 6 months left on my 3 year warranty and I sent it in. About 10 days later I get my unit back with no problem found. Hmmm.... They suggest unplugging the auxiliary water pump as it tends to give the Climate Control fits (if not damage the unit) if it has seized.

I test the system with and without the aux pump plugged in. I still think my Climate Control unit is the issue and send it back in. The folks at Programa must have felt sorry for me and send me back another unit (exchange) as a courtesy. Nice customer service – it makes me feel better at least.

So by the time the next Climate Control came in I have a new auxiliary pump installed (and I did a monovalve rebuild kit at the same time since it's all on the same bracket). No difference. Programa said the next suspect part to investigate would be the Blower regulator or the temperature regulator. It took me some looking, but I found both of these parts attached to either side of the blower under the glove box.

This past week or so I also diagnosed and replaced two of my switchover units (#1 and #3) on that common vacuum rail thingy. Now I'm able to get air through the center vents on max (push button setting right of the defrost setting), but as soon as I push the normal A/C button, the center vents slip close. With the glovebox liner out I can watch the flaps behind the glove box open on max and slowly slip close on normal A/C. If I put a vacuum directly on the pink egg vacuum pod thingy deep in the center of the dash (hooking directly to the orifice that leads to the #3 switchover), it won't hold vacuum. So I assume that pink / green pod diaphragm is shot????

Tonight as I tried to see what flaps were working the climate control was really doing odd things. I had the car running and set the climate control on Max A/C (temp dial all the way blue), and the compressor never kicks on. I just get cool outside air. When I move the dial all the way to heat I hear a weird little cycling sound and no heat (or blower speeds). I turn off the engine but keep the key engaged and I track the cycling hum to the monovalve opening and closing fairly quickly. Super weird! I give the car a few minutes break. Start it up again and I get the compressor to kick in and A/C runs cold and the heat works as well. I swear it's possessed!

So.... back to my maddening climate control. Do you think it is the blower regulator or temperature regulator, both.... or something else?

__________________
~shell
As of 2/2010:
2001 CLK55 0o\=*=/o0
13.6 @ 106mph
10K mi
1984 300SD
260K mi and going and going...
97 S600
46K miles
1991 Sentra SE-R (extremely dorked with)
www.se-r.net

Last edited by bodyart27; 12-14-2005 at 10:01 AM.
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  #2  
Old 12-13-2005, 10:42 PM
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Usually the evap temp sensor either works or wont work. It just senses temp and passes voltage along. I had on go bad one time and kept the hole system from coming on. Use a volt meter and test what its doing and how many volts.
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  #3  
Old 12-13-2005, 10:58 PM
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Join Date: Nov 2002
Location: Dallas
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Need some more clarification...

So I found a picture of the evap temp sensor - but where is it on the car? Is it easy to test?

I will say that I think the roof sensor is working as I can either cover it with my hand to generate a little heat to make the A/C kick on, or shine my flashlight on the roof sensor to create a little heat to kick the fan speed up when I'm trying to get the A/C to kick on.
__________________
~shell
As of 2/2010:
2001 CLK55 0o\=*=/o0
13.6 @ 106mph
10K mi
1984 300SD
260K mi and going and going...
97 S600
46K miles
1991 Sentra SE-R (extremely dorked with)
www.se-r.net
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  #4  
Old 12-14-2005, 10:00 AM
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Join Date: Nov 2002
Location: Dallas
Posts: 802
Drive this morning....

Coming to work with the pushbutton unit on Econ (cool outside), blower didn't come on and at a stop light I could hear the Monovalve cycling.... so weird. I just turned the unit off and kept driving.
__________________
~shell
As of 2/2010:
2001 CLK55 0o\=*=/o0
13.6 @ 106mph
10K mi
1984 300SD
260K mi and going and going...
97 S600
46K miles
1991 Sentra SE-R (extremely dorked with)
www.se-r.net
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  #5  
Old 12-14-2005, 01:06 PM
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Location: Lathrup Village, Michigan
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I've never heard the monovalve cycling and don't believe that it is audible inside the car.

I have found that my keyswitch can go too far over and the climate control will not work anymore.

The diaphram insert for pod #3 does look like it needs to be replaced.

The blower speeds are also controlled by the temperature control module if in auto mode. The temperature control module also controls some of the vacuum pods.

It looks like I need to finish my climate control tester...
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Michael LaFleur

'05 E320 CDI - 86,000 miles
'86 300SDL - 360,000 miles
'85 300SD - 150,000 miles (sold)
'89 190D - 120,000 miles (sold)
'85 300SD - 317,000 miles (sold)
'98 ML320 - 270,000 miles (sold)
'75 300D - 170,000 miles (sold)
'83 Harley Davidson FLTC (Broken again) :-(
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  #6  
Old 12-14-2005, 09:35 PM
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Join Date: Nov 2002
Location: Dallas
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monovalve cycling

It is weird. I actually got out of the car and put my hand on the monovalve to make sure that was what was making the sound (dude that puppy was HOT!).

So, the temperature control module that you are referring to, is that the box attached to the right of the blower?
__________________
~shell
As of 2/2010:
2001 CLK55 0o\=*=/o0
13.6 @ 106mph
10K mi
1984 300SD
260K mi and going and going...
97 S600
46K miles
1991 Sentra SE-R (extremely dorked with)
www.se-r.net
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  #7  
Old 12-14-2005, 10:02 PM
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Join Date: Sep 2001
Location: Lathrup Village, Michigan
Posts: 2,939
Quote:
Originally Posted by bodyart27
It is weird. I actually got out of the car and put my hand on the monovalve to make sure that was what was making the sound (dude that puppy was HOT!).

So, the temperature control module that you are referring to, is that the box attached to the right of the blower?
That's the one.

I bought a used temp controller on eBay and it fixed some of my problems, but not all.
__________________
Michael LaFleur

'05 E320 CDI - 86,000 miles
'86 300SDL - 360,000 miles
'85 300SD - 150,000 miles (sold)
'89 190D - 120,000 miles (sold)
'85 300SD - 317,000 miles (sold)
'98 ML320 - 270,000 miles (sold)
'75 300D - 170,000 miles (sold)
'83 Harley Davidson FLTC (Broken again) :-(
'61 Plymouth Valiant - 60k mikes
2004 Papillon (Oliver)
2005 Tzitzu (Griffon)
2009 Welsh Corgi (Buba)

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  #8  
Old 12-14-2005, 10:42 PM
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Join Date: Jul 2004
Posts: 7,381
Quote:
Originally Posted by mplafleur
I've never heard the monovalve cycling and don't believe that it is audible inside the car.

I have found that my keyswitch can go too far over and the climate control will not work anymore.


The diaphram insert for pod #3 does look like it needs to be replaced.

The blower speeds are also controlled by the temperature control module if in auto mode. The temperature control module also controls some of the vacuum pods.

It looks like I need to finish my climate control tester...

I have found that my keyswitch can go too far over and the climate control will not work anymore
. I found this also F*&^S with the climate control- there is a spring on the ignition, try moving the key a bit counterclockwise when you have problems and see if this makes a difference.
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  #9  
Old 12-14-2005, 11:13 PM
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Join Date: Nov 2002
Location: Dallas
Posts: 802
keyswitch?

Ignition key? Interesting! I'll give that a try!

__________________
~shell
As of 2/2010:
2001 CLK55 0o\=*=/o0
13.6 @ 106mph
10K mi
1984 300SD
260K mi and going and going...
97 S600
46K miles
1991 Sentra SE-R (extremely dorked with)
www.se-r.net
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