a/c dead on 560sl

[sms]

Hi,

My a/c has been not working for awhile. R12 has all leaked out. Gages read 0 for high and low side. Believe it is the compressor since there is a dirty oil residue on it, but the dirt could just be normal road dirt. Anyway, I partially charged it with a substitute refrigerant (just for finding the leak) that contained a flourescant dye. I got the pressure up to 60 on the low and 50 on the high side, but could not get the compressor to kick-in even when I shorted out the pressure switch. Refrigerant leaked out in 1 day and was unable to see the dye anywhere with a black light.

Why couldn't I get the compressor to kick-in and could the leak be in another component other than the compressor? How should I proceed?

Thanks!

Okay. One can of refrigerant will not put enough pressure in the system to allow the compressor to kick in. The low pressure switch shuts off the compressor to protect it from low refrigerant level. Without adequate refrigerant, lubricant does not circulate, thus will destroy the compressor.

So now you have contaminated the system with whatever "alternate" refrigerant you added to the system. There are all sorts of problems involved when introducing incompatible refrigerants and oils. If the oil is incompatible it will not circulate thus destroying the compressor. If the refrigerant mixes with another refrigerant or moisture acids will be created that will eventually eat a hole in the evaporator or other components.

Had you not contaminated the system, you would have been able to simply find your leak, repair it and recharge with R12. Now that the system is contaminated, you will have to break all connections, THOROUGHLY flush the system, remove the compressor and pour out the mineral oil, then put in the correct amount of oil, replace the filter drier, evacuate and recharge.

This will be necessary regardless of the refrigerant you choose. You only have to go through this process if you want to have a system that will live for a long time. There are other things that people do all the time to get a/c, but most of them are short term solutions.

It's amazing how $30 per pound refrigerant cost causes people to do all sorts of things that cost them hundreds or thousands of dollars. Penny wise and pound foolish.

Since you are at this point now, if you are lucky the pressure that is in the system will force some of the UV dye out where you can see it. Start at the easy to see connections and around the compressor shaft seal.

Good luck,

[sms]

Larry,

I used 2 cans of enviro-safe w/ dye to charge my system and I was under the impression that it was compatible with the oil already in my system. What I was trying to avoid was not just wasting the r12, but also not leaking it to the environment once I was done with the leak detection.

I believe that I now know why the compressor didn't engage, but you can tell me if I'm wrong. Being a recent Mercedes owner, I forgot the meaning of some of the controls and had the climate control set on "non-cool" and not cool. Later today I'll try again, but my refrigerant my be all gone by then which leads me to believe that it may have leaked out from some other place than the compressor (ie. leak is fast). Is the orifice tube located behind the glove compartment and is it worth checking now?

Steve

Two cans should have been enough to engage the compressor. Whether it was or wasn't, if it has leaked out since the dye was put in, there certainly should be enough dye traces to find the leak. The most difficult would be if you can not run it and the leak is in the evaporator. If you can't find a leak anywhere else, aim your UV light at the vent in darkness and see if you can get the blower to blow past the evaporator. You might can see UV dust coming out if it is dark enough and your black light is powerful enough.

Good luck,

[sms]

Larry,

Do you still think that I must flush the system or can I just pump it down once I fix the leak?

Thanks again!

Steve

Since you have put in this foreign refrigerant, the system is contaminated. You will now have to completely flush the system, replace the filter drier, flush the compressor with oil, put in the correct amount of oil, turn the compressor by hand after system is together to distribute the oil away from the compressor to prevent liquid lock, evacuate and charge.

Good luck

[sms]

Larry,

I got the compressor to kick in by overiding the pressure switch on the receiver/dryer. The pressure on low side only got up to 70 psi and high was less than 50 psi. This was with adding 2 cans of refrigerant w dye! I checked for leaks with a black light on the compressor/condenser and inside the car around the vents, but didn't see anything! Any thoughts on my next steps? Does the low pressure on the high side indicate a big compressor leak?

Thanks,

Steve