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  #1  
Old 04-24-2004, 04:01 PM
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Join Date: Mar 2004
Location: Charleston, SC
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A/C problems confounding me

Did a search and did not see anything that fit what I am seeing.

Situation:

134 conversion was done when I bought the car. Fan motor and fan speed select switch replaced. System charged. Took approx. 2 cans of refrigerant.

A/C blows cold for the first minute or so and then cycles between cold and hot at about 15 second intervals.

Any ideas what the problem could be?

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  #2  
Old 04-24-2004, 05:34 PM
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Pull the glove box and replace the foam hose between the plastic pipe coming from the grille beside the sunroof switch and the interior temp sensor. Make sure the little fan down there works, too.

Also, if the hose is OK or replacing it doesn't fix things, you may need to re-solder the pushbutton control unit. The solder joints crack, and this will cause intermittant cycling -- if the switchover valves behind the glove box are constantly clicking, this is the problem.

Peter
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  #3  
Old 04-25-2004, 11:16 AM
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Didn't see a "foam" hose. There was the large plastic one going into the heater core, a vacuum line with some foam around it where it crossed behind the heater core line and the bundle of green and red vacuum lines right on the bottom just behine the front lip of the glove box opening, but no "foam" hose. It sounded like it was cycling but it sounded like the compressor, not the switchover valves you spoke of.
It seemed to blow much colder today and not get warm between cycles like it did the other day.


Think of anything else I could look at????
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  #4  
Old 04-25-2004, 02:13 PM
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Clean the sight glass on the reciever/dryer and check for visible bubbles while the compressor is running. If you see some, the system is probably undercharged, so the suction side pressure drops too low, the evaporator starts to freeze up, and the temp switch kicks the compressor off until the evaporator thaws. You will also see ice rather than condensation on the expansion valve if this is the case.

I don't know where the expansion valve is on the 190, though.

Normal charge for a Benz AC is more like 3 cans, though (85% by weight of what the sticker says for R12).

Peter
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1972 220D ?? miles
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1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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  #5  
Old 04-25-2004, 02:59 PM
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The plot thickens

No bubbles and no ice.

I did notice though that the air stayed cold and there was no cold/warm/cold cycling. The difference is, I left the window down so I could stick my hand in and check the temp of the air. Blew ice cold for 5 minutes straight without cycling. Only does it when the car is zipped up. Climate control is set to lowest temp setting.
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  #6  
Old 04-25-2004, 03:48 PM
it leaks, its german
 
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You never said if you experienced this driving and if it was universal to all the vents.




Just for yucks pop the cowl cover off, look to the right of the wiper assembly and you'll see the heater control valve. If the side vents are going hot and the center stays cold the valve is opening. Its vacuum controlled therefore you'd want to trace the vacum circuit. Sounds like a vacuum problem to me.



Joe
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  #7  
Old 04-25-2004, 05:52 PM
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Already fixed the hot on the sides cold in the middle thing. I don't get hot out of any vents now with the AC on. My point of the last post was to get some comments on what might be the problem with it working fine with the windows down and cyceling on and off with the car buttoned up.

Still looking for some suggestions.
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Sunroof
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Smoked corners
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  #8  
Old 04-26-2004, 04:02 PM
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bump.

Still need help here guys, this one is baffeling me.
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Smoked corners
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  #9  
Old 04-26-2004, 04:42 PM
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I checked three sources for your R-12 capacity for your car and found the following:
1.) 2.2 lbs
2.) 34 oz.
3.) 38 oz.

This would give an avg. amount of ~ 36oz. of R-12. Using 85% to 90% of this figure to arrive at the approx. R-134a amount comes to approx. 30 oz.

If you used approximately two 12oz. cans you have 22-23 oz. of R-134a in yor system. This is a fairly significant undercharge on this size system. Weight charging, on a retrofit, isn't that reliable though, and some gauge pressures at 1500-2000 rpm would tell us charge status. I'd like about 220psi/30-35psi on an 80F day @1500-2000 rpm with windows open and CCU set at "min" and blower on high.

I'm NOT saying that an undercharge accounts for your symptoms, but I'd start off there, before moving down the diagnostic tree. Undercharged systems trigger some oddball protective "faults" quite often. FWIW Good luck

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Last edited by jbaj007; 04-26-2004 at 06:08 PM.
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