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  #1  
Old 05-12-2000, 11:09 AM
Coming back from burnout
 
Join Date: Jun 1999
Location: in the Pacific Northwest
Posts: 2,274
1.The problem turned out to be the AC switch where the green-blue wire wasnt getting 12 V signal I think its supposed to get from Blower motor wire when you want AC on. Everything else checked out fine on the switch; the dampener opener grounds out like it should, the temp function works also.
2.Question 1: Like a dummy, worrying about under lubrication, I stuck 3 oz. oil in the new Reciever. Afterthought makes me wonder if I covered Dessicant in it and destroyed its Drier /Moisture removing function?
3. Question 2. Where can we order a ternary switch to protect from over pressure? For the time being I am going to use a home wired Pressure switch with reset from a pneumatic shop at the high pressure charging side with a relay to shut the compressor down. I'm calibrating it to 250 psi, reset = 35 psi. Is that the right setting?
4. Question 3. What is the right side to charge the system from--low or hi?
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Old 05-12-2000, 09:35 PM
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Join Date: Mar 2000
Location: Gainesville FL
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I was all set to go on this one until question number 4 slapped me in the face.

How can a technician with a conscience give advise to anyone who could ask question number four. There is safety and other issues here.

As a result my only answer is that the current (since 1985) low pressure switch is also a high pressure switch. It handles both issues. MB# 124 821 36 51 or 124 820 80 10. Both numbers are from memory I might be wrong about the second one. These are both the same part from different vendors and are interchangable.

------------------
Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician
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  #3  
Old 05-13-2000, 12:56 AM
Coming back from burnout
 
Join Date: Jun 1999
Location: in the Pacific Northwest
Posts: 2,274
I was told the present pressure switch is a low pressure switch only.If it has a high pressure switch fcn then my job is done.
..a wise person will always take advice and be humble and keep his or her mouth shut.Anybody who is a Mercedes Master Tech with 26 years experience (and hard work!) and runs a business must be very intelligent and capable and has my ultimate respect.
Respectfully,
Richard Chang
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  #4  
Old 05-13-2000, 12:56 AM
Coming back from burnout
 
Join Date: Jun 1999
Location: in the Pacific Northwest
Posts: 2,274
I was told the present pressure switch is a low pressure switch only.If it has a high pressure switch fcn then my job is done.
..a wise person will always take advice and be humble and keep his or her mouth shut.Anybody who is a Mercedes Master Tech with 26 years experience (and hard work!) and runs a business must be very intelligent and capable and has my ultimate respect.
Respectfully,
Richard Chang
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  #5  
Old 05-13-2000, 06:57 AM
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Join Date: Jun 1999
Location: Los Angeles, Calif, USA
Posts: 521
Richard,

Are you glad that you bring up the question? I do not want the system blow up in front of your face when you charging it from the high side. It is a very high pressure system - high enough that can kill you when things go wrong.

I heard the news last year that a group of students having a BBQ party of some kind. One student threw an unopen can (beer?) into the fire and it explosed killing one of his friends. I, at one time, tried to unmount a 14 inch tire from a wheel. After I put the tire on a tire machine, I should deflate it by removing the valve. I did not do that but tried to cut the rubber slightly to deflate it. It was only 30 psi pressure but I underestimated the power of air pressure. It exploded. Thing happened so quickly that I did not hear the noise of explosion but I felt my face was wet (due to the water inside the tire). My hair got wet also and went straight up. My hand was numb. The knife flew away. One of my pockets on my coverall flew away too. One of my sleeve came off the coverall. I lost 90% of hearing both ears the first hour, 50% hearing at the end of the day. It took two weeks to get all my hearing back.

You possibly had fun reading my story but it was a good lesson for me. Otherwise, next time I may not be that luck. There is always a danger of A/C hose rupture. Wear protective glasses when work on the A/C under the hood. Improper usage of the charging equipements is very dangerous. Learn enough about it before you start.

David

[This message has been edited by be459 (edited 05-13-2000).]
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  #6  
Old 05-13-2000, 02:15 PM
Coming back from burnout
 
Join Date: Jun 1999
Location: in the Pacific Northwest
Posts: 2,274
...but you know, some AC systems are charged from the High Side> I've seen documentation on it several places. Look on any Interdynamics Gauge Box or the Haynes AC manual. Intuitively, to me it sounds wrong. I mean the high side at 200 psi could blow out the can! But the reason I asked is Mercedes does evrything different than any other car I've worked on--fuse box in engine compartment, timing chain, I thought maybe this was another example of this...
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  #7  
Old 05-13-2000, 02:47 PM
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Join Date: Mar 2000
Location: Gainesville FL
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OK its like this. If you have a charging station you can charge from either side with the system OFF!!! In this state both sides of the system are the same pressure so it doesn't matter.

Actually in these type recharges the system is filled by driving liquid from a higher pressure vessel to one of lower pressure. This only works if you have a large reservoir of pressure not a single can. After charging in this method it would be dangerous to start the car immediately if one had charged through the low side; as there would be liquid refrigerant on the intake side of the compressor.

Most people (even with good charging stations) charge through the low side as it takes less time when there is a large pressure differential.

One thing you must remember is that the pressure of a container of refrigerant is only determined by the temperature not the quantity. ie: Five pounds of refrigerant in a thirty pound cylinder will have the same pressure as one pound in your inactive system. In order to get refrigerant into an inactive system you must fill from the bottom flowing liquid and measure the weight so you can stop way before the pressures equalize. If you were to fill from the top the pressures would equalize before a full charge occured.

------------------
Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician
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