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  #16  
Old 05-05-2004, 08:19 PM
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Location: central Texas
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Very interesting....
I am glad you got that information before I put mine together...
Trey is who I got my R12 block valve from...
I had never heard of unwinding and clamping to that sensor line...
Thanks...

Of course here in Texas me and Larry are allowed to fret over the little stuff....
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  #17  
Old 05-05-2004, 09:01 PM
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When Trey mentioned that the capillary tube is clamped to the suction line he was speaking in general terms and did not say this was the case specifically with a 300D. I don't think it could apply to my exp valve with such a short capillary tube.

In the MB shop manual the insulation for the expansion valve and cap tube looks like a formed insulating shell, not insulating tape wrap as is used when the exp- valve is replaced by a mechanic. Maybe their original designed insulating shell allowed the cap tube to sence the temp of the exp valve or, it was to prevent or contain condensation from forming on the block and dripping in the car.

good luck!
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Last edited by erubin; 05-05-2004 at 09:09 PM.
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  #18  
Old 05-05-2004, 11:05 PM
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I just disassembled the spare TXV I've been holding onto for a "project". Unscrewing the round brass plug you can pull out a spring tensioned ball valve actuated by a two piece rod going thru the length of the TXV from the aerobic capsule/capillary tube to the ball valve under the plug.

The first piece of rod moves when the capsule/capillary gas expands, affected by the temperature of the gas EXITING the
TXV.

The first piece pushes the second length of rod thru an orifice that only grossly controlls the amount of refrigerant ENTERING the TXV. This part is not controlling much at all; it's just mostly a passageway.

However, the end of this rod (under the brass screw plug) pushes on the ball valve which is under spring tension. The amount of tension is determined by the amount the round plug is screwed or unscrewed into the TXV body. The amount that this ball is lifted off it's seat is what really controls the amount of refrigerant ENTERING the evaporator and it is controlled by the temperature of the refrigerant gas EXITING the evaporator (acting on the capsule which acts on rod # 1, which acts on rod #2, which acts on the ball, which chills the capsule, which shortens the rod #1, which.........oh, what the heck). A nice simple feed-back.

Bottom line is the plug seems to be able to control it to conform to most any regular refrigerant gas.

IF YOU ADJUST THE PLUG TO ALLOW MORE REFRIGERANT INTO THE EVAPORATOR YOU RUN THE VERY REAL RISK OF "SLUGGING" AND RUINING YOUR COMPRESSOR SINCE LIQUID REFRIGERANT CAN GET TO IT (low/no superheat). FWIW
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Last edited by jbaj007; 07-28-2006 at 01:34 AM.
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  #19  
Old 05-06-2004, 09:52 AM
LarryBible
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Yes, originally the expansion valve insulation was a dry foam. The standard field insulation is Presstite tape. It is important to insulate it.

The mercury tube on many expansion valves clamp to the low side line with insulation, but the mercury tube on these H Block expansion valves is self contained and makes contact with the block.

I guess there may be some aftermarket units with longer mercury tubes that can or should be fixed in place.

Good luck,
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  #20  
Old 05-06-2004, 10:10 AM
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"The amount that this ball is lifted off it's seat is what really controls the amount of refrigerant ENTERING the evaporator and it is controlled by the temperature of the refrigerant gas EXITING the evaporator (acting on the capsule which acts on rod # 1, which acts on rod #2, which acts on the ball, which chills the capsule, which shortens the rod #1, which.........oh, what the heck). A nice simple feed-back." ---Jbaj007

This is what I was saying lately in the discussion with JC.....
That this is the primary way in which our systems control the temperature in the evaporator... as compared to it being the low side pressure per se ... because you can have a vacuumed tank which is hot.... the cooling effect is from the phase change happening in the evaporator... and this is a mechanical self regulating feedback system....with electrical cutouts for safety of the parts running from mainly the R/D connection....
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  #21  
Old 05-06-2004, 12:11 PM
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My foam insulation fell apart in my hand when getting to this Tx valve....
"makes contact with the block"... with the ' block valve body' or are you saying it should be touching the evaporator or something else ?

If it is wrapped with a good insulation.... I wonder if this interfers with the aerobic compensation provided through the pin hole?

Why does the pigtail have a hole in it ? Why would the diaphram need to be barometric pressure compensating to read the temperature ?

I realize that ice forms at other than 32 degrees sometimes... that that is based on a standard barometric day at a certain humidity...29.92.... etc.... but is this what the pin hole in the pig tail is supposed to be working with to control it that close at the bottom end ?
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