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Old 07-31-2001, 09:12 PM
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Unhappy A/C blows warm air!

I have a 1984 MB 300 TD the A/C worked fine last summer. But it now just blows warm air. I took it to the machenic. First he told me it was the A/C compressure. So he replaced it with the new one along with the Dryer. He also put in the R-12. After all that done, the problem still exists. He came back and told me that the evaporator is also the problem. At this point I don't have any more confident in him. Could anybody tell me if I need a second opinion? or could anybody tell me what is the source of A/C problem? The machenic also mentioned something about the pipe might have cloqqed up that might lead to the damage of the Evaporator. Like I said I lost fate in this guy... Please help...

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Old 07-31-2001, 09:27 PM
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Cryoseal for AC?

I went for about a year and a half w/o A/C in my 91 300E. My Freon was leaking out after about a month, so after some checking we determined there was probably a pin hole in the Evaporator coil. After determining what the cost would be to replace the coil, (app. $2700 done right) I decided heat was fine. I heard about a product called Cryoseal ( which is supposed to fix holes from the inside. After much reluctance by my mechanic and research on my part, I decided to take the risk and try it out. So far (after about a month) I am still cool....but who knows what the future holds. The entire operation cost me about $1000.00. But I paid extra for labor since my mechanic had never done it before and I basicaly had to twist his arm to do it. I can only hope it works for the long haul...time will tell.
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Old 07-31-2001, 11:26 PM
Senior Member
Join Date: Apr 2001
Location: Beech Island, S.C.
Posts: 468
In my 30 years experience and it might be just a coinsidence I have never replaced the evaporater in a 300D. Plenty compressors, condensers, expansion valves but no evaporaters. Get a second opinion before patching something that does'nt leak.
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Old 08-01-2001, 08:50 AM
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Thank you Stan. That's what I'm going to do , get a second opinion
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Old 08-01-2001, 09:35 AM
Registered User
Join Date: Jan 2001
Location: Northern Virginia
Posts: 46
Hey there,

I admit I'm not too familiar with the 300D model, but I know that on my 300E that had the same problem, it was that the aux fan was not running while the A/C was on. It MUST run. without the additional cooling capacity of the aux fan, pressures on the high side get way high, and the refrigerant never cools significantly to get cool air out of the evaporator. Check your "ballast resistor" mine looked like a little beige rectangular block, trace the wire back from the fan and you should find it, mine is located on the drivers side fenderwell under the abs controller. Also the aux fan relay in the fuse box may be bad, but if the fan isn't running when the a/c is on, check the resistor first, then the relay. There is also a pressure switch on the receiver drier that activates the fan when the a/c is on. your mech should have checked for leaks, another one may do a better job. They should be able to put the ultraviolet die in and use a black light to pinpoint a leak.

Good luck
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Old 08-01-2001, 09:19 PM
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Join Date: Jun 1999
Location: Los Angeles, Calif, USA
Posts: 521
By monitoring the pressure of the high and low sides and observing other physical characteristics, your mechanic should be able to tell where the problem is. If the system was working last year and not working now, the chance of having a leaking system is very high.

What tests did he do telling him that you had a bad compressor and a clogged "pipe"? The 300D has other control devices also controlling the temperature. They need to be tested too in a logical manner.

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Old 08-02-2001, 07:09 AM
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Don't overlook the monovalve. The late 123 cars are known for the heater control valve diaphragm rupturing causing heat in the heater core overcoming the cold evaporator air.

In case you're not familiar with the monovalve, it is on the firewall next to the battery with heater hoses in and out. Take the four screws out of the top and lift it up to see if the diaphragm is ruptured. If so, you can get a repair kit from the parts shop or your dealer for around $30.

Good luck,
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Old 08-02-2001, 11:49 AM
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To All,

I'd like to thank you all for your inputs. This has been a great research/experience for me. I feel that I had gained some experiences. I should be able to talk more intelligently when I go back to the mechanic. I will keep you all informed.

Again, Thank you


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