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Old 05-08-2000, 03:23 PM
Gregg Vurbeff
Posts: n/a
My '78 300d A/C has been out for some time now. My mec. says I need a new compresser and rec/dryer. He also wants to convert it from R12 to R134. I have asked around about this process and have had mixed answers. Some say no problems with the conversion, others say that the R134 puts more pressure (30psi) into the system and the molecules are smaller therefore leaks will happen. Has anyone converted to the newer R134 and what are your results? Any other comments??

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Old 05-08-2000, 08:08 PM
CMuc's Avatar
Join Date: Jul 1999
Location: Port Coquitlam BC, Can
Posts: 92
I converted my 87' 300E to 134A two years ago. I live in Vancouver B.C. and it became illegal to charge with R12. The climate control works great except when the temp. is above 28C and stuck in traffic. I have made some inquiries here and suspect the condensor isn't efficient enough. Every spring I perform an evacuation and re-charge on the system and have not noticed a significant loss of refrigerant.

Chris Muc
Auto Tech
'87 300E 338,000 km
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Old 05-08-2000, 09:56 PM
Registered User
Join Date: Mar 1999
Location: Suwanee, GA, USA
Posts: 4,712
The compressor you have should be able to handle the pressures. I would replace the hoses with the barrier type. The 134 is actually larger in molecular size, this is why we use a 75 to 80% charge ratio to 12. Good luck with the conversion.

Be sure the temp switch is taken off of the drier and a trinary (late style aux fan switch is installed) . This will turn on the aux fan quickly and help with high pressure.

Donnie Drummonds
1992 500E (very soon I hope
1981 280GE SWB
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Old 05-11-2000, 12:29 AM
Gregg Vurbeff
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HELP!! I went out and purchased the late style temp. switch but it will not fit the rec./dryer. My mec. said that it's a good idea but it will not fit the rec./dryer. Any suggestions??
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Old 05-11-2000, 12:48 AM
Gregg Vurbeff
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I forgot to mention that my mec. said that the original switch is O.K. and he's never had any problems with overheating of the system. I tried to find a trinary???? switch. No one has heard of such a switch. I went and called everywhere but again no one has heard of the trinary switch. I even explained the three points that the switch accomplished. The MBZ dealer said that more than likely it's an aftermarket part plus MBZ dosen't recommend the conversion. Any help would be GREATLY appreciated.

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