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Old 07-14-2004, 01:24 AM
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Join Date: Dec 2003
Location: new jersey
Posts: 181
a/c leak, apply vacuum or pressure?

I am a beginner at a/c repair. please pardon me in advance if my approach is beneath the exoerienced here. system lost refrigerant due to leak at least 2 years ago and was down when i purchased the car. previous diagnosis from repair shops claimed leak from evaporator. i find that unlikely as looking at the part it looks like a simple aluminum housing, not much going on. also in reading different MB material, i found these things hardly ever leak. perhaps hoses or connections to the evap fail but not the unit itself. so i will try to tackle it myself one staep at a time. my first priority is to find and stop the leak.
I understand that if the leak is small then i can apply vacuum, fill with refrigerant/dye and start looking for the leak. is this just a matter of getting a vacuum pump from pep boys and hooking up to low pressure side?
if the leak is big then it won't hold a vacuum. in that case i understand that i should apply pressure and look/listen for the leak. is this also just a matter of getting a pump from pep boys and hooking to low pressure side?
thanks for any responses.

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Old 07-14-2004, 09:50 AM
Posts: n/a
Some of your questions are general, but you really should let us know the year and model car that you are working on. I think I speak for all of us here at mshop, we are terrible mind readers.

You are generally correct to a point. One way to find the leak is to charge with UV dye, but there again without knowing the year and model, we don't know what refrigerant is used.

If it is a large leak, it will still most likely not be large enough to hear. The best approach for that is to pressurize with nitrogen and a few ounces of R22 then use an electronic leak detector to "sniff" for the leak.

There are some MB's that have a terrible problem with their evaporators and they are difficult to change. Others have bulletproof evaps and are easy to change.

Year and model please,
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Old 07-14-2004, 05:37 PM
Registered User
Join Date: Dec 2003
Location: new jersey
Posts: 181
thanks for the response.
car is 1985 380sl.
it was never converted so i am dealing with r-12.
from the directions in the cd shop manual, it seems the car was built around the evaporator.
does your response still hold (to charge with nitrogen and few ounces of r-22)? i have a battery operated electronic leak detector. can i purchase a pressurized canister of nitrogen and r22 at the local automotive store or pep boys?
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Old 07-14-2004, 09:59 PM
Posts: n/a
No, you'll have to find an a/c tech. Maybe you know someone who does home a/c repair. They can pressurize with nitrogen and give it a few ounces of R22.

Since you have a sniffer, you might could just put a couple of ounces of R22 in and sniff. If it is a good size leak, there will be enough pressure from just a few ounces that you will probably be able to find the leak. Then it will be verified. If you can't find it that way you won't be able to rule out the leak until you do something further.

But, if it is a profuse leak R22 alone will probably allow you to find it.

Good luck,

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