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1984 Mercedes-Benz 300DT; 1980 Mercedes-Benz 300SD
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Discussion Starter · #1 ·
Finally got my A/C up and running, had to change the compressor after all, also replaced the drier while at it, went ahead and went with the r134 route (I know I know, r12 is best), my question is, how many ounces (lbs?) of freon does the system take?

My Haynes manual say nothing about its capacity, and the searches I've pulled say either 2, or 3lbs?


I put 36oz (3, 12oz cans), its pretty cold, but could it be colder (on r134 of course), I've been told that I should be able to see a steady stream of bubbles on the drier, which should stop after a few seconds if there is enough freon, the bubbles on my drier keep going....

Thanks again folks!
 

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'82 300D
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That is for R-12. You need to go by the high and low side pressures based on ambient temps. Too much R-134 results in too high pressures and reduced cooling capacity.
 

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77 240d, 02 Ford F250 V10 (7mpg), 05 GMC Denali (The Baby Hauler), 2000 BMW 323CI (was my Bros car)
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2.5 lbs is about right.
 

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1984 Mercedes-Benz 300DT; 1980 Mercedes-Benz 300SD
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Discussion Starter · #6 ·
Is it ok to mix refrigerent brands? Or is r134 the same all around, the r134 I purchase is now out of stock, and they (parts store) are saying they probably wont carry it anymore, cant find it online either....
 

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W-1-2-3 Go!
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2.6lbs R12

(if you're using R134a will you have to increase the amount due to the smaller molecules, and if so how much R134a should you add?) :)
 

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1984 Mercedes-Benz 300DT; 1980 Mercedes-Benz 300SD
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780 Posts
Discussion Starter · #8 ·
Thanks for all the input, its amazing how many types of freon, kits, retrofit things, etc... they sell, but nothing about capacities at these auto part stores.

Aftermath:

Ok, so with 36oz in the system, bubbles were constantly flowing on the drier window, and the gauge reading was about 32-35psi, I put about 6-8 ounces more, for a total of about 42oz (2.6lbs) in the system, drove it around the block... now the gauge reads between 26-30psi, but now I can see bubbles every once in a while on the drier window..

If I put more freon in, why did the psi drop? shouldn't it have gone up?
 

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79 240 D - 82 300 D - 79 300SD - 96 dodge cummins
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take it for what its worth. I am no ac specialist, But I do know that the higher the psi the warmer your ac blows. so if the pump is cycling and you add more R134A it won't blow as cold.
 

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1984 Mercedes-Benz 300DT; 1980 Mercedes-Benz 300SD
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Discussion Starter · #10 ·
Its pretty chilly now, I think the extra 6-8oz's did the trick, I'm just not going to mess with it now, will cross my fingers it'll last aslong as I own the car
 

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1982 300 D Turbo Diesel
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For what it's worth, I recently re charged my A/C system. My 300D is a fairly recent purchase and it has been a northern car and I don't think that the A/C was really used. Anyhow, I have put approx 3lbs of R134 in and so far so good. My vents are throwing snowballs and life at this point is pretty good. :) Now I just need to find out why I have a diesel/exhaust smell coming from the vents.
 

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Discussion Starter · #12 ·
Thanks! I'm running about 4-6oz's less then yourself, doubt it will make that much of a difference, guess I should of just dumped 4 entire cans in it.
 

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'82 300D
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The chart does not go by pounds and ounces, that is why you did not see it. It goes by pressure at ambient outside temps measured infront of the a/c condensor.
 

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1984 Mercedes-Benz 300DT; 1980 Mercedes-Benz 300SD
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Discussion Starter · #14 ·
Thanks rrgrassi, but how would know exactly how much r134 the system needs then?
 

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Keep track of how much was used to achieve the proper pressure.

IIRC, the max fill for R-12 was 2.6 pounds. R134a should be about 10% less. Do not use the sight glass for charge indication when using R134a or other refridgerants.
 

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Discussion Starter · #16 ·
Keep track of how much was used to achieve the proper pressure.

IIRC, the max fill for R-12 was 2.6 pounds. R134a should be about 10% less. Do not use the sight glass for charge indication when using R134a or other refridgerants.


I've been told its the opposite, there should be more R134a then there was R12?? :confused:
 

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Discussion Starter · #18 ·
Thanks, already asking questions on it, just to clear things up.

karugs, where did you hear about adding more r134a due to molecule size?


KC 123, with 3lb of freon in there, what are your LOW pressure readings if you dont mind me asking?




--
 

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I've been told its the opposite, there should be more R134a then there was R12?? :confused:
Whoever told you that was simply wrong.:mad:

Flush the system COMPLETELY using SOLVENT, add 8 oz of POE oil, change the drier, the expansion valve, and use 2-3 cans of 134 with guages. You should see 200 high side pressure and 35 on the low. If you're lucky the sight glass will turn clear on a cool day.

It's depressing to see how many IGNORANT people there are who claim to understand the black art of air conditioning.:surrender:
 
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