AC stopped blowing cold air - R12 91 560SEL - Mercedes-Benz Forum
 
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post #1 of 6 (permalink) Old 06-15-2019, 02:32 PM Thread Starter
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AC stopped blowing cold air - R12 91 560SEL

My AC just stopped blowing cold air. Clutch appears to be engaging normally but just blowing ambient air. Below are my guage readings

Static while engine is off
Ambient Temp = 60F
Low side = 40 psi
High side = 40 psi

Running system pressures with engine at op temp
Low side = 3 psi
High side = 75 psi

My conclusion is I may have a bad compressor. My question is should I try and add R12 freon and see if the issue is resolved? Do you have a different analysis based on the pressure readings above?

Thank you
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post #2 of 6 (permalink) Old 06-15-2019, 03:57 PM
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When I got my '87 560SEL with the bad AC, I was quoted $1300 to fix it with a rebuilt compressor and that was 15 years ago. Turns out that a little sleuthing showed the compressor was leaking and "not from the front". That meant where the refrigerant lines connected were the leak. There are four o-rings in that connection block and two more on the lines. The two o-rings in the high pressure side were bad so for about $6.00, I put in six new o-rings.

Said all that so I could say this - are you sure it's the compressor that's bad? If it's just a leak, get a batch of miscellaneous AC (green viton) o-rings and some Ester Oil for R12 to lube each o-ring as it's installed, and replace all you can get to. My SEC had six of thirteen connections with bad o-rings.

I filled my SEC and SEL refrigerant systems with propane (aka R290) and run pressures of 35 & 200 psi. Very cold air!!

Blasphemous Mike
US '87 560SEC with Euro headlights, clear markers, H&Rs, 17x8.5/Nitto's, ATE slotted rotors with ceramic pads, BergWerks FGS, 3.07 Limited Slip. '87 560SEL with Euro Headlights, lowered, 235/40/17's
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post #3 of 6 (permalink) Old 06-15-2019, 03:58 PM
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I think it always makes sense to re-charge the system with a little dye and see if it is just leaking tubes.

R12 on Ebay $20-40 per can. Lots of mechanics pretend it is much more.
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post #4 of 6 (permalink) Old 06-15-2019, 07:13 PM Thread Starter
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would like to add that there are bubbles in the sight glass as well. In this case, the freon is low and might be caused by a leak. Does this make sense?
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post #5 of 6 (permalink) Old 06-15-2019, 07:54 PM
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If you see bubbles, yes its low, you could add a pound and inject UV dye, the leak cant be too bad if its still holding some freon. Once the bubbles disappear, its fullly charged. REMEMBER, if you open it up to replace orings you have to vacuum it out for an hour (depending on how strong the vac pump is) You know to add freon into the low side, as a gas, not a liquid. Systems leak with age naturally, so maybe you dont have a serious problem. Also you will need an R12 can piercing tool.
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Last edited by ot1; 06-15-2019 at 07:58 PM.
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post #6 of 6 (permalink) Old 06-15-2019, 09:12 PM Thread Starter
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Thank you. Any suggestion on what type of dye leak detector to use for r12?
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