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  #16  
Old 04-24-2011, 09:08 PM
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It's a 1980 w116. It has AccII with an UnwiredTools servo replacement. The heater circuit has a ball valve to positively turn it off during the summer. I have the same expansion valve as shown above in post 3. Temperature was measured using my VOM meter with the temperature probe placed against the evap pipe.

Vent temps are around 47-50 degrees as measured with the doors closed and the system on recirculate.

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  #17  
Old 04-24-2011, 11:06 PM
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Quote:
Originally Posted by thorsen View Post
...Vent temps are around 47-50 degrees as measured with the doors closed and the system on recirculate.
Are the windows open ?
Do you have some sort of ' helper fan ' putting air into the front of your car on the condensor ?
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  #18  
Old 04-25-2011, 10:37 AM
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Windows are closed.

I have the aux fan on and a large fan blowing right on the condenser.
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  #19  
Old 04-25-2011, 10:51 AM
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So you have a Combo Block TXValve ( as compared to the suction fitting you mentioned earlier ? )just like the rest of us.... ?

You are measuring the temperature at that item with a probe which may be not be ideal for use against a small metal surface..... I am only familiar with using that type of probe for HVAC vents in houses where the entire probe end would be subject to what is being measured.....Is that mentioned somewhere reliable as a legit tool for measuring there ?

Are you measuring at a place between the Evaporator and the TXvalve ? And you are sure that it is the EXIT tube from the Evaporator ?

How about running the test again with the windows open ?

And you are absolutely sure that no hot coolant is making it to the heater core since it is turned off manually ?
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  #20  
Old 04-25-2011, 11:20 AM
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A picture of my expansion valve is attached. I don't know what type it is.

I doubt my use of the probe is approved in any of the repair manuals, but I was using it more of a relative measure, ie- the suction fitting at the compressor is 22* but the fitting at the evap is 50*.

I am 100% sure I measured the exit from the evap because I checked it before and after the oil return line. The oil return line is the small line from the side of the valve that has a threaded connection on it. It attaches to the suction line after the evap.

I am also 100% sure there is no coolant flow. I checked the pipes leading into the core and they were not hot.
Attached Thumbnails
116.120 Climate Control Issues:-txv.jpg  
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  #21  
Old 04-25-2011, 11:29 AM
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So you pretty much have new everything...

What was the situation which caused you to renew most of your AC system ?

Can you get that probe to different spots on the evaporator ?

Have you cleaned or inspected the coils of the evaporator for cleanliness ?

How about trying to find where , relatively, the pfcondensor changes the refrigerant from gas to liquid... hopefully about half way down the coils..
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  #22  
Old 04-25-2011, 11:56 AM
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In a classical AC system you would have NO parts which are below freezing...
You have a line near the compressor cold enough to make ice...
so the Txvalve... more specifically the siphoning throttle valve part of it was certainly suspect since that is supposed to keep the evaporator from getting below freezing so that ice will not form from the humidity in the air passing across the fins of the evaporator and Stopping air flow....
but here you seem to have it warmer at the exit of the evaporator ... than at the downstream fitting at the compressor... Since the theory is that changing the liquid at the TXvalve to spray into the evaporator is what allows heat to be absorbed from the warm air flowing across the fins... something is clearly wrong.
There is not a physics theory which would allow it to get colder after exiting the evaporator while going along that line to the inlet side of the compressor...
So I am hoping your method of measuring the temp at the exit line of the evaporator is not giving true results... otherwise I am totally out of ' theory ' ....

If on the other hand... your evaporator is dirty enough to keep the warm air from the car from taking away enough cold to operate the exit side of the txvalve... then it is possible for properly cold fluid to exit the evaporator .... along with the possibility the txvalve is not functioning properly.... and the line be below freezing at the inlet to the compressor...
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  #23  
Old 04-25-2011, 12:09 PM
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Correct, with the exception of the evap everything is new. When I restored the car the AC was inop and out of freon so I replaced everything I could get to. The evap is pretty well hidden and I can only touch a small part of it near the end. I have not cleaned it due to accessibility restrictions. The part I can touch is cool but not super cold.

I have a pretty basic understanding of the theory but I can't come up with anything that fits my symptoms. I was thinking that a partially plugged evap might be the problem but that wasn't explaining my higher-than-should-be low pressure.
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  #24  
Old 04-25-2011, 12:15 PM
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So at this time... to summarize..

1. We are dealing with a totally new untested TxValve.
2. We might have a dirty evaporator fin condition. ( did you see Dmorrison's thread?)
3. We DO have frost which should not be extant anywhere....
4 We have frost at the wrong place theory wise if your temp at the exit of the evap is true.

I have no theory which fits all your symptoms either ....

" just waiting for Superman or woman to arrive and save the day... "....

Last edited by whunter; 04-25-2011 at 06:01 PM. Reason: spelling
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  #25  
Old 04-25-2011, 02:04 PM
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That summarizes it.

My plan is to remove the evap, but if I go that far I might as well replace it instead of just cleaning it. A new receiver/drier is mandatory and a new expansion valve makes sense too. I'm trying to decide if I should pull the Sanden and put in a Seltec compressor (personal preference) and be done once and for all.

Thanks for your help.
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  #26  
Old 04-25-2011, 02:18 PM
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Sorry I could not find the answer... I am sure you are going to really examine all the parts as they come out to try to resolve the mystery.....and post anything you find out....
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  #27  
Old 04-25-2011, 03:19 PM
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Thanks for your help troubleshooting.

The one thing I wasn't sure about - should the sight glass still have refrigerant visible in it when the compressor cycles? Or is it OK that after 3-4 seconds I see bubbles then no refrigerant?
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  #28  
Old 04-25-2011, 03:30 PM
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If you read over on air condition dot com... and the FSM MB AC manual.. you might just totally ignore the sight glass.... many professionals consider it useless for the purpose of charging the system .... it can be useful for some other purposes but I do not remember which exactly....
There are combos of variables which make it potentially unreliable with regards to bubbles......
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  #29  
Old 04-25-2011, 04:20 PM
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Quote:
Originally Posted by leathermang View Post
I will bet that you do not even KNOW what the conditions are which might cause the sight glass to indicate ( by still having bubbles ) more refrigerant was needed ( when it is actually full )
Wow. Someone must have peed in your coffee cup this morning.

Quote:
Originally Posted by leathermang View Post
Come on !!! it is an open book test and I will bet you can not even find and tell us what they are.....
Pointeless argument. I have 37°F in the vent. Regardless of who you side with in theory, the results speak for themselves.

Quote:
Originally Posted by leathermang View Post
If you did know them...( very unlikely.... given your defense of ' I have been doing it this way for x number of years and it worked for me ' ) how simple and KIND it would have been to list them when you said that...
I just shared what worked for me. I am sincerely sorry I didn't ask you for your blessing first.

Quote:
Originally Posted by leathermang View Post
Others reading this should keep in mind that the MB AC FSM WARNS against just using the sight glass as the method for filling because it can give erroneous readings...
Hmmmm....Not in the W116 manual, and not in a few other MBZ manuals I have here.

Since you dismiss anything anyone other than yourself states, I will simply direct your attention to he MBZ publication:

Section 85-314 in the W116 CC II Manual States: "Fill until refrigerant flows free of bubbles past the sightglass in the receiver drier..."

Please write to MBUSA and tell them they are wrong.

Quote:
Originally Posted by leathermang View Post
"SO EASY !!! SO SMART AND KIND to others who might not have the background to understand that you are depending on luck instead of what the makers of your car go to the trouble of researching and printing in the instruction manual....
LOL!!!!

The same luck that your local MBZ techs rely on!!! Have you ever worked in a flat-rate shop????

I hope your day gets better....Robert
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  #30  
Old 04-25-2011, 04:29 PM
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My manuals were published in the early 1980's .... perhaps between 1978 and then they learned from some people that it was possible under certain conditions to have the sight glass give a false ' add ' reading...and cause serious damage....and included that in their AC manual.
So you never used the 2 mm movement of the number one intake valve on the number one cylinder for anything either.... is that an indicator of some larger trend in your life ?

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