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  #1  
Old 08-05-2009, 11:31 PM
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AC Question. Still HOT in Houston. Need expert opinion!

w123 85 Cali,

I'd love to have some working AC. Here's the problems I'm having at the moment. I find these symptoms to be a little outside the norm.

Just after starting the engine, the line in front of the valve cover gets chilly, even starts sweating. The air out the vents in the cabin begins to drop... as low as 75 (hot hot day). I think it would go MUCH lower, but then the problems start. After a few minutes, everything begins to warm back up; air out the vents in the cabin climbs up to a balmy 85, and the line in front of the valve cover stops sweating and gets warm.

I've tested the pressure at this line at several intervals, and it always checks out and stays consistent.

My KLIMA (I think) is bad. Never turns the compressor off. What could be causing things to start out so nice then turn all wrong?

Checked the mono-valve. It WAS stuck, but I un-stuck it. Didn't fix the problem.

OVP relay fuse replacement is next on my list, followed by a new KLIMA. I don't think these fixes will assist in supplying cold(er) air though.

Thoughts? A little unusual, I think.

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  #2  
Old 08-05-2009, 11:46 PM
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mmmmmm Diesel...
 
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When the cold (suction line) gets warm, is the compressor still engaged? Does your Aux fan turn on?

You could have a plugged drier or faulty expansion valve. The mono vlve cold be stuck again, but it would not affect the suction line getting warm again. The getting warm again means freon may not be flowing, or some how bypassed the evaporator by means of a faulty expansion valve. I do not know if a bad expansion valve lets freon by pass the evap.
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  #3  
Old 08-06-2009, 07:15 AM
LarryBible
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Pull the glove box and check the hose that goes from the sensor just below the small square grill in front of the dash, over to a pipe behind the glove box. If it has disappeared or rotted, get a piece of rubber hose from Home Depot or somewhere that will connect these two pieces.
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  #4  
Old 08-06-2009, 08:22 AM
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Quote:
Originally Posted by rrgrassi View Post
When the cold (suction line) gets warm, is the compressor still engaged? Does your Aux fan turn on?
Yes. The compressor is ALWAYS on. Even when I turn the controls off. I'm sure it's a faulty KLIMA or CCU. Again, the system remains pressurized.


Quote:
Originally Posted by rrgrassi View Post
You could have a plugged drier or faulty expansion valve. The mono vlve cold be stuck again, but it would not affect the suction line getting warm again. The getting warm again means freon may not be flowing, or some how bypassed the evaporator by means of a faulty expansion valve. I do not know if a bad expansion valve lets freon by pass the evap.
Plugged drier. Perhaps. Monovalve is still functional. Yeah, perhaps the expansion valve. What does the pressure switch do? Could it be at fault as well?

Dang! All these options sound like I will be evacuating the system.
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  #5  
Old 08-06-2009, 09:00 AM
LarryBible
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or not...
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  #6  
Old 08-06-2009, 09:30 AM
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Quote:
Originally Posted by LarryBible View Post
or not...
Ah-ha! Indeed. One can only hope.
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'82 300TDT --- 236,xxx miles --- (My first one) Sold July '09
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  #7  
Old 08-06-2009, 10:02 AM
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mmmmmm Diesel...
 
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If the compressor is running, the suction line should be cold.

Do check the foam tube in the dash. I replaced mine with foam that lines water pipes an home A/C pipes.
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70's SPM #5608 Fairmont A-4 MOW car

06 VW Jetta TDI 280K miles

03 VW Golf TDI 5 speed 400K Miles Engine died

RIP--Lost in fire...82 300D 322K was My Daily Driver-On the search for a w126 now...

90 Dodge D250 5.9 Cummins/5 speed. 400K
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  #8  
Old 08-06-2009, 10:25 AM
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Quote:
Originally Posted by LarryBible View Post
Pull the glove box and check the hose that goes from the sensor just below the small square grill in front of the dash, over to a pipe behind the glove box. If it has disappeared or rotted, get a piece of rubber hose from Home Depot or somewhere that will connect these two pieces.
Larry, will this not simply control cycling of the compressor using the cabin temperature as the parameter?

If the compressor runs all the time, none of the electrical controls can be the culprit..........???
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  #9  
Old 08-06-2009, 10:27 AM
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Quote:
Originally Posted by scoodidabop View Post
Yes. The compressor is ALWAYS on. Even when I turn the controls off. I'm sure it's a faulty KLIMA or CCU.


Are you certain that you understand when the compressor is rotating? Have you observed it in a condition when it was not rotating (with the engine running, of course)?

If you pull the Klima, the compressor cannot rotate...........
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  #10  
Old 08-06-2009, 11:18 AM
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Has any repairs been done on the system recently where some moisture could have entered?

What you describe could be a symptom of moisture freezing in the expansion valve.
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  #11  
Old 08-06-2009, 11:40 AM
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Could the clutch on the compressor be frozen? That would explain the always-on compressor. You can pull the electrical connector (2 pins) at the compressor, see if the compressor sill runs. If it doesm the clutch is frozen. If it does not, the problem is upstream, something (Klima?) telling the clutch to always be engaged.
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  #12  
Old 08-06-2009, 12:42 PM
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More data needed

Quote:
Originally Posted by scoodidabop View Post
w123 85 Cali,

I'd love to have some working AC. Here's the problems I'm having at the moment. I find these symptoms to be a little outside the norm.

Just after starting the engine, the line in front of the valve cover gets chilly, even starts sweating. The air out the vents in the cabin begins to drop... as low as 75 (hot hot day). I think it would go MUCH lower, but then the problems start. After a few minutes, everything begins to warm back up; air out the vents in the cabin climbs up to a balmy 85, and the line in front of the valve cover stops sweating and gets warm.

I've tested the pressure at this line at several intervals, and it always checks out and stays consistent.

My KLIMA (I think) is bad. Never turns the compressor off. What could be causing things to start out so nice then turn all wrong?

Checked the mono-valve. It WAS stuck, but I un-stuck it. Didn't fix the problem.

OVP relay fuse replacement is next on my list, followed by a new KLIMA. I don't think these fixes will assist in supplying cold(er) air though.

Thoughts? A little unusual, I think.
Bypass the heater core or Pinch off the heater hoses for this testing, if the vent temperature suddenly drops = a bad mono valve..

What is the operating system pressure (engine running)?
What is the static (engine off) system pressure?

If the system pressure is correct.
Educated Guess:

Evaporator temperature sensor (two male spade connectors)
MB# 003 820 24 10

This sensor commands compressor cycling to prevent evaporator core freeze up/ice.
When the Evaporator temperature sensor fails CLOSED = the compressor will NOT cycle = the evaporator core becomes a block of ice = no cold air flow.

#1. Remove the glove box pocket.
#2. Disconnect one of the two male spade connectors.
#3. Start engine.
#4. The compressor should now be off.
#5. Use an infrared thermometer on the evaporator vapor line (return = large) to get a temperature base reading (write down the temp).
#6. Connect the wire you removed for one minute, and repeat step #5 (write down the temp).
#7. Wait one minute, repeat step #6 for two minutes, and repeat step #5 (write down the temp).
#8. Wait one minute, repeat step #6 for three minutes, and repeat step #5 (write down the temp).
#9. Wait one minute, repeat step #6 for four minutes, and repeat step #5 (write down the temp).
#7. Wait one minute, repeat step #6 for five minutes, and repeat step #5 (write down the temp).
Etc, etc,etc, up to fifteen minutes, if the evaporator temperature sensor is working, the compressor should cycle several times, and the output line temperature will stabilize somewhere above 36 F.




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  #13  
Old 08-06-2009, 12:47 PM
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Quote:
Originally Posted by whunter View Post
This sensor commands compressor cycling to prevent evaporator core freeze up/ice.
Roy, he states that the compressor is not cycling.........running all the time.
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  #14  
Old 08-06-2009, 06:21 PM
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Yes

Quote:
Originally Posted by Brian Carlton View Post
Roy, he states that the compressor is not cycling.........running all the time.
I only added the diagnostic if he wanted to test before replacing
Evaporator temperature sensor (two male spade connectors)
MB# 003 820 24 10

If the evaporator out put line temperature keeps dropping below 36 F = the evaporator temperature sensor is junk.
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  #15  
Old 08-07-2009, 12:06 AM
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Quote:
Originally Posted by Brian Carlton View Post
Are you certain that you understand when the compressor is rotating? Have you observed it in a condition when it was not rotating (with the engine running, of course)?

If you pull the Klima, the compressor cannot rotate...........
Indeed I do understand. I've pulled the KLIMA and noted it's appearance, then reinstalled KLIMA to see the compressor engage. It's definitely on as long as the KLIMA is plugged in.

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'90 300SE --- 173k miles --- (Odometer just stopped working!)

'85 Cali 300D --- 193500 miles --- (Second one) Sold Nov '10

'82 300TDT --- 236,xxx miles --- (My first one) Sold July '09
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