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  #1  
Old 09-03-2008, 10:49 AM
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Unhappy A/C Gemlin Lives

87 300E a/c is acting poorly despite best efforts and limited acumen: (Make that a duh!)

A/C functions reasonably well while rolling down the road, but doesn't want to cool well at all while sitting at an idle

What I have done:
flushed multiple times
All fluids fresh
replaced drier/receiver and switches
tested pressure ok (exc on high side but not so on the low side)
no leaks
fan ok
new expansion valve didn't impact situation...

Rather than guess any further or simply throw parts at the impasse, thought someone here might provide a "Eureka moment" for me.
And yes, it's damn hot in Florida in the Summertime.....and humidity in between hurricanes is even worse....:-)

Thanks in advance for any help.

-j

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  #2  
Old 09-03-2008, 10:54 AM
michael cole's Avatar
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have you cleaned out the condensor and radiator.pressure washed might work best.also check your visco fan clutch for proper operation
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  #3  
Old 09-03-2008, 11:07 AM
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Unhappy A/C gremlins

Clean flushed radiaotr-condenser four times although not pressure washed...fan clutch appears to be operational.
Both were nasty....
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  #4  
Old 09-03-2008, 12:04 PM
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sounds like you have covered the basics.next on the list would be checking the freon charge.you mentioned pressures are good but refigerant is charged by weight.so i would recommend evacuation and recharge to spec.if you dont have the equipment see your trusted local a/c guy
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  #5  
Old 09-03-2008, 12:17 PM
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Are you still using R12? Is the sight glass clear at idle? What are the pressure readings at idle? At idle you should see the high side go up, the aux. fans turn on to cool the condensor, and high side drops. Repeat.
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  #6  
Old 09-03-2008, 12:48 PM
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You mentioned that the low side pressure isn't right - If the low side pressure is low, it is a for sure indication that the refrigerant charge is low. Watch your sight glass and have someone turn on the AC - you should see bubbles, then clear as the refrigerant becomes a liquid on the high side of the compressor. Feel the return line to the compressor with the fan on a high setting - it should be cool to cold going into the compressor, if it feels warm there's not enough refrigerant charge.

If you have converted to R-134, be aware that now the condenser is 1/3 too small for the rest of the system. You would see a huge performance gain by going to a parallel flow condenser.
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'01 ML320
'82 300D 4.3L V6/T700R4 conversion
'82 380SL, '86 560SL engine/trans. installed
'79 450SL, digital servo update
'75 280C
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  #7  
Old 09-03-2008, 07:09 PM
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Yes, the conversion has been made to 134. Would you care to explain the condenser parallel system for me in easy to understand terms? 1/3 less?
Thank you....and all comments are greatly appreciated.

-j
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  #8  
Old 09-05-2008, 10:48 AM
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Hi there,
Probably the easiest way to get an explanation is to put the following argument in google: Parallel flow condenser. That will pull up a bunch of sites that talk about the differences in the single flow and parallel flow condenser, with pictures. The Parallel flow condenser has up to 5 times the surface area for the refrigerant to come into contact within the pipes, which allows the heat to be drawn off the R134 much more effectively, and (very important) allows the system to run at a lower temperature, which helps prevent thermal runaway, which is a condition that converted systems can have - if the condenser cannot liquefy the R134 before it leaves, there will be vapor getting to the expansion valve, which causes more heat, which can take out the compressor. If you don't want to replace the condenser I recommend that you wire the fan temperature switch so that the aux fan is always on when the compressor is on, which will help considerably.

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'01 ML320
'82 300D 4.3L V6/T700R4 conversion
'82 380SL, '86 560SL engine/trans. installed
'79 450SL, digital servo update
'75 280C
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