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Old 06-05-2007, 08:15 AM
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Join Date: Mar 2006
Location: Detroit, MI
Posts: 79
A/C conversion

I have a 1987 560 sl and I am about to change my ac compressor and drier. I already installed the new expansion valve. I want to convert it from R12 to R134. What does it take to convert the system over to the newer refrigerant? I have the rebuilt compressor and new drier waiting to go in.

1987 560 SL "The Beast"
1999 Jeep Cherokee Sport
2003 Nissan Altima
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Old 06-05-2007, 09:51 AM
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Join Date: Sep 2004
Location: DFW / Collin County Texas
Posts: 1,882
Do a search here - there's a lot of discussion about conversion. You could read for hours, no, for days on end. Here are the basics:

* R12 is not scarce and is not unjustifiably expensive.
* conversion will require that every single component of the A/C system be disassembled, flushed completely, reassembled (preferably with new o-rings), and then recharged with the correct oil and refrigerant. For best results, expansion valve should be replaced with one specifically designed for use with R12. Sometimes this can be hard to find because manufacturers don't typically make R134a expansion valves for cars not originally designed to use it.
* conversion will result in a system that performs less efficiently than if you just leave everything the way it is. On a 95 degree day, my R12 car puts out 38 degrees at the vent whereas my R134a converted car puts out 48 degrees, and can slowly climb to 58 degrees when the vehicle is not moving. Depending on where you live, you might not care too much about this. Installing a P-flow condensor can help.
* conversion will put a much higher load on your compressor; a typical R12 system runs at about 200 to 225 psi on the high side, whereas a converted R134a system might run about 350 to 375 - premature compressor failures (especially with rebuilt units) are not at all uncommon.
08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280
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Old 06-05-2007, 10:33 AM
I told you so!
Join Date: Jun 2002
Location: Motor City, MI
Posts: 2,853
R134 should work okay up here in Detroit. But I agree that r12 is not as expensive as it once was and it's probably prudent to stay with r12.

Make sure to replace all o-rings, and it would be a good idea to add UV dye to the system before buttoning everything back up.
95 E320 Cabriolet, 159K
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Old 06-05-2007, 02:29 PM
just-n-time's Avatar
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Join Date: Feb 2006
Location: Louisiana266 Maloy Rd winnfield71483
Posts: 804
Not to burst any ones bubble,Look I gave my wife a 90,420sel AC,was not working,it had a crack in the hose from the drier to the evaporator, i replaced the drier and hose,evacuated the system for 24 hours,reinstalled freon (freez 12) and have not had a moments trouble.The air will freez you out.I keep it set at 70 and it gets very cold.By the way I live in Central LA.
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Old 06-05-2007, 04:47 PM
I told you so!
Join Date: Jun 2002
Location: Motor City, MI
Posts: 2,853
Freeze12 is a blend of 80% r134a and 20% r142b. The r142b is to carry the mineral oil. So you're essentially running r134a refrigerant.
95 E320 Cabriolet, 159K
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Old 06-05-2007, 04:55 PM
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Join Date: Jul 2001
Location: Western Michigan
Posts: 1,080
Let me throw in my two cents because I just had my 1991 300E AC recharged with R12.

There is a mandatory check for leaks before recharge so that was $40. Indy said the GOV won't let them just pump in R12 into the system.

The system was low on R12 via pressure check. There was no noticeable leak. However, the Indy insisted on

1) recover the R12
2) evacuate the system
3) weigh how much R12 was recovered
4) fill the system with capacity which was 2.5 lb
5) put in UV dye.

Mine was low by 1.5 lb and the R12 alone was $84. The recovery/evacuate/fill was another 1 hr of labor ($65). So my total bill was $206.

I went back for the free black-light check and there was no leak.

I do not know if the recovery/evacuate is completely necessary. He might be able to fill some R12 based on pressure but he said the way he did it was the right way.
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Old 06-06-2007, 10:27 AM
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Join Date: May 2006
Location: Bradenton, FL
Posts: 286
Ww Iii

As we discussed, R12 is best to stay with.


Bob Jones
Bradenton, FL
'87 560SL-Sold
'99 SL500 For Now
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