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Discussion Starter #1
I would really appreciate some advice concerning my A/C. It will only cool down to about 60 degrees F. I have a standard A/C, not Climate control on my 1983 240D. The system is fully charged and pressures look good. The compressor seems to cycle too often to me. The Recirculating flap is working properly and, both heater cables are adjusted correctly. When I first turn the A/C on, it cools down to 50 degreees but then gradually increases to 60 or 65 degrees. Any ideas? Thanks, Cliff
 

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2008 PT, 1998 neon--1965 VW 1200
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2,533 Posts
are you driving to get these results?

ive found that my a/c cools much better if i revv the engine if the car is just idling(the ac sucks alot of power, i might roll down the windows instead!!)

im sorry its not more help. i do know that someone was posting asking how many of our air conditioners were actually cold a little bit ago. this leads me to believe that they dont work too well/long/often=)
 

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Discussion Starter #3
The results are while driving. A friend of mine has practically the same car and his A/C is putting out 40 degrees F. I feel like I am overlooking something simple. This A/C is relatively unsofisticated. Cliff
 

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1982 280E
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Hi Cliff,

I'm afraid that your post is a bit too generic. The A/C is indeed not a very sophisticated system, but there are a number of checks that you need to do in order to diagnose your system.

The first thing that I would recommend is to evacuate the system, flush it properly, replace the expansion valve and receiver/dryer and refill. This should take care of any crap that may have collected in the system over the last 20 years or so...

Secondly, check that your interior air temperature sensor is working. Although I have never messed with it myself, I read a number of posts about this little rubber hose behind the dash that may be loose, giving a false temperature reading. On the other hand, this is more likely to give too much cooling than too little.

Yet another thing to check is if the temperature sensor in the evaporator core is plugged in and working. Your symptoms may point to an evaporator that actually freezes up and therefore lets less air through. Again this is a guess without the proper checks...

I hope this helps....
 

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240D
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You said "The system is fully charged and pressures look good" but you didn't state the system pressures. It certainly sounds like you have a clogged expansion valve, which might let a bit of pressure through initially, but stop up as flow increases, thus reducing the cooling. You SHOULD be able to see this with gauges, because initially pressures on the downstream side (the larger pipe) will go up, then taper off while system is running. This would also explain the compressor cycling, because it cycles off at max pressure.

Good luck and let us know what the answer to the problem turns out to be.
 

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1981 300D
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Please post your operating pressures at start-up idle. Then let it run for 3-5 minutes to stabalize system & note pressures & any variances then idle up to about 1500r.p.m. & hold her steady keep an eye on pressures & sight glass if equipped, there should be a few random bubbles I believe. Sight glass will be down on accumulator & may be painted. It should be right on top,hex shaped with a round indentation inside the hex shape & if it is painted gently scratch off paint, of course you might want to do the whole sight glass thing before you start her up to recoed pressures. Then we can go from there. Without seeing pressures it's hard to diagnose but right now i"m leaning toward expansion valve problem.Maybe clogged or out of adjustment if adjustable. could also be temp sensor but you can tell by watching pressures.What pressures do you have when comppresor us cycling on & off?
 

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1981 300D
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benmaples - 3/22/2005 4:22 PM also are your condensor & radiator fins clean.

Please post your operating pressures at start-up idle. Then let it run for 3-5 minutes to stabalize system & note pressures & any variances then idle up to about 1500r.p.m. & hold her steady keep an eye on pressures & sight glass if equipped, there should be a few random bubbles I believe. Sight glass will be down on accumulator & may be painted. It should be right on top,hex shaped with a round indentation inside the hex shape & if it is painted gently scratch off paint, of course you might want to do the whole sight glass thing before you start her up to recoed pressures. Then we can go from there. Without seeing pressures it's hard to diagnose but right now i"m leaning toward expansion valve problem.Maybe clogged or out of adjustment if adjustable. could also be temp sensor but you can tell by watching pressures.What pressures do you have when comppresor us cycling on & off?
 

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Discussion Starter #8
Hi everyone, I wanted to post an update. I did fix my A/C ! It turned out to be the evaporator Temperature sensor. Once I replaced it, my compressor started running longer and the sytem now cools to about 50 degrees which, i guess is as good as it is going to get. My system pressures are 25/200 with the compressor engaged and 30/250 when it is not. Do these seem OK? Thnaks, Cliff
 
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